Sa'd ibn Mu'adh
Sa'd ibn Mu'adh (Arabic: سعد ابن معاذ) (c.591-627) was the chief of the Aws tribe in Medina and one of the prominent companions of the Islamic prophet Muhammad. He died shortly after the Battle of the Trench.
He married Hind bint Simak, his agnatic second cousin,:329 whose brother had been chief of the Aws tribe until he was killed at the Battle of Bu'ath.:470 They had two sons, Amr and Abdullah.:329
As'ad ibn Zurarah, chief of the al-Najjar clan of the Khazraj, was Sa'd's maternal first cousin.:473 Usayd ibn Hudayr was his wife's fraternal nephew,:329 and was also said by al-Waqidi to have been Sa'd's first cousin.:440
Acceptance of Islam
Sa'd was among the leading figures among the Ansar, as Muhammad had dubbed the people of Aws and Khazraj from Medina who converted to Islam. He converted at the hands of Mu'sab ibn Umar. His conversion led to the immediate conversion of his entire subtribe of the Aus, the Banu Abdul-Ashhal:
“The leader whom his people follow has come to you” As’ad said Mus’ab. So Mus’ab said to him what he had said to Usayd, Sa’d stuck his lance into the ground, and sat down. The same thing happened again [ie. Conversion to Islam] and he went to his people’s meeting place accompanied by Usayd [who had converted earlier]. When they saw him coming they said: “We swear by Allah, Sa’d has returned with a different impression.” And when he reached them he asked them how they knew what had happened to him. They replied “You are our Chief, the most active in our interests, the best in your judgement, and the most fortunate in leadership.” He then said: “I will not speak to a man or a woman among you until you believe in Allah and his Apostle.” As a result every man and woman among the Banu Abdul-Ashhal joined Islam. 
Confrontation with Abu Jahl and start of Badr hostilities
Prior to the Battle of Badr, Sa’d had visited Mecca once to perform his Umra with his non-Muslim friend Umayah ibn Khalaf, when they came across Abu Jahl. They had an argument, and as it became heated, Sa'd threatened Abu Jahl with preventing his safe passage through Medina if he stopped the Muslims from performing pilgrimage in Mecca. Narrated 'Abdullah bin Mas'ud:
From Sa`d bin Mu`adh: Sa`d bin Mu`adh was an intimate friend of Umaiya bin Khalaf and whenever Umaiya passed through Medina, he used to stay with Sa`d, and whenever Sa`d went to Mecca, he used to stay with Umaiya.
When Allah's Messenger (ﷺ) arrived at Medina, Sa`d went to perform `Umra and stayed at Umaiya's home in Mecca. He said to Umaiya, "Tell me of a time when (the Mosque) is empty so that I may be able to perform Tawaf around the Ka`ba." So Umaiya went with him about midday. Abu Jahl met them and said, "O Abu Safwan! Who is this man accompanying you?" He said, "He is Sa`d." Abu Jahl addressed Sa`d saying, "I see you wandering about safely in Mecca inspite of the fact that you have given shelter to the people who have changed their religion (i.e. became Muslims) and have claimed that you will help them and support them. By Allah, if you were not in the company of Abu Safwan, you would not be able to go your family safely." Sa`d, raising his voice, said to him, "By Allah, if you should stop me from doing this (i.e. performing Tawaf) I would certainly prevent you from something which is more valuable for you, that is, your passage through Medina." On this, Umaiya said to him, "O Sa`d do not raise your voice before Abu-l-Hakam, the chief of the people of the Valley (of Mecca)." Sa`d said, "O Umaiya, stop that! By Allah, I have heard Allah's Messenger (ﷺ) predicting that the Muslim will kill you." Umaiya asked, "In Mecca?" Sa`d said, "I do not know." Umaiya was greatly scared by that news.
When Umaiya returned to his family, he said to his wife, "O Um Safwan! Don't you know what Sa`d told me? "She said, "What has he told you?" He replied, "He claims that Muhammad has informed them (i.e. companions that they will kill me. I asked him, 'In Mecca?' He replied, 'I do not know." Then Umaiya added, "By Allah, I will never go out of Mecca." But when the day of (the Ghazwa of) Badr came, Abu Jahl called the people to war, saying, "Go and protect your caravan." But Umaiya disliked to go out (of Mecca). Abu Jahl came to him and said, "O Abu Safwan! If the people see you staying behind though you are the chief of the people of the Valley, then they will remain behind with you." Abu Jahl kept on urging him to go until he (i.e. Umaiya) said, "As you have forced me to change my mind, by Allah, I will buy the best camel in Mecca. Then Umaiya said (to his wife). "O Um Safwan, prepare what I need (for the journey)." She said to him, "O Abu Safwan! Have you forgotten what your Yathribi brother told you?" He said, "No, but I do not want to go with them but for a short distance."
So when Umaiya went out, he used to tie his camel wherever he camped. He kept on doing that till Allah caused him to be killed at Badr. 
Battle of Badr
The Muslims originally expected a much smaller Meccan force, but were surprised by the large Meccan Army so the Prophet called Shura:
When the Muslim army missed the caravan and the Quraysh army, between nine hundred and one thousand strong, helmeted and drawing closer, Abu Bakr stood up and said something good.
Several more Muhajirin also spoke, all the while the Messenger of Allah repeated: "advise me, O Muslims!", inquiring of what the Ansar, the majority then, had to say.
Then Sa`d bin Mu`adh said, "It looks like you mean us, O Messenger of Allah! By He Who has sent you with the Truth! Never think that we will leave you to fight alone, if it is even out of bonds.
And I take a Oath with you as the head of Ansaar, You give us what you want, You Collect from us what we have. You take us any where you want, you push us in any battle, We will defend you, defend till our last breath. No arrow can touch you, before it passing form our chests. We have tied a relationship of life and death with you. If you seek to cross the seas or go in it, We will follow Your Command and none among us will remain behind. We are patient in war, vicious in battle. May Allah allow you to witness from our efforts what comforts your eyes. Therefore, march forward with the blessing of Allah.
Then Miqdad RA continued... By God ! We will not say, as the disciples of Prophet Moses (Jews) said "You and Your Allah go and fight with infidels, we are sitting right here." We will surround your left, right, front, back and protect you in every cause and every battle. We will die first, before enemy reaches you.
We would not dislike that you lead us to meet your enemy tomorrow.
The Messenger of Allah was pleased with the words of Sa`d and was encouraged to march on. 
Battle of Uhud
Sa'd was one of the few companions who remained on the battlefield, when the Meccans led Khalid bin Walid counterattacked and continue fight on until he was finally forced to retreat away from the Meccans. Infact, Sa'd was the last Muslim Mu'sab ibn Umar met (Sa'd by that time had disengaged the Meccans) when he chided other Muslims for retreating and ferociously attacked the Meccans resulting in his brutal martyrdom at the hands of the Meccans.  He later met up with Muhammad and was part of the small contingent Muslims defending him.
Battle of Trench and Qurayza
After the Battle of the Trench in 627 (5 AH), when Medina was unsuccessfully besieged by the Meccan army, the Banu Qurayza had treacherous dealings with the enemy. Later the Muslims laid siege to their stronghold and the Banu Qurayza surrendered unconditionally after several weeks of siege.
Several members of the Banu Aus pleaded for their old Jewish allies and agreed to Muhammad's proposal that one of their chiefs should judge the matter. The Banu Qurayza themselves appointed Sa'd, and declared they would agree with whatever was Sa'd's verdict. The verdict was consistent with the Bible[note 1] and some scholars claim the verdict was based on the Bible.
Some people (i.e. the Jews of Bani bin Quraiza) agreed to accept the verdict of Sad bin Muadh so the Prophet sent for him (i.e. Sad bin Muadh). He came riding a donkey, and when he approached the Mosque, the Prophet said, "Get up for the best amongst you." or said, "Get up for your chief." Then the Prophet said, "O Sad! These people have agreed to accept your verdict." Sad said, "I judge that their warriors should be killed and their children and women should be taken as captives." The Prophet said, "You have given a judgment similar to Allah's Judgment (or the King's judgment)."
Sa'd had been wounded in the earlier battles, and was on the verge of death. Sa'd succumbed to the wounds and died after returning to Medina.
He dutifully served as a member of the Muslim community and even commanded military campaigns for the Prophet during his lifetime. Saad is said to have been a stern, just and passionate man, willing to impulsively fight for what he believed in. In Muslim history, he is well regarded as a noble companion who enjoyed a close relationship with the Prophet.
I heard the Prophet saying, "The Throne (of Allah) shook at the death of Saad bin Muadh." Through another group of narrators, Jabir added, "I heard the Prophet : saying, 'The Throne of the Beneficent shook because of the death of Saad bin Muadh."
Even after his death Muhammad made constant references praising him:
A silken cloth was given as a present to the Prophet . His companions started touching it and admiring its softness. The Prophet said, "Are you admiring its softness? The handkerchiefs of Sad bin Muadh (in Paradise) are better and softer than it."
- When you march up to attack a city, make its people an offer of peace. If they accept and open their gates, all the people in it shall be subject to forced labor and shall work for you. If they refuse to make peace and they engage you in battle, lay siege to that city. When the Lord your God delivers it into your hand, put to the sword all the men in it. As for the women, the children, the livestock and everything else in the city, you may take these as plunder for yourselves. And you may use the plunder the Lord your God gives you from your enemies. This is how you are to treat all the cities that are at a distance from you and do not belong to the nations nearby. However, in the cities of the nations the Lord your God is giving you as an inheritance, do not leave alive anything that breathes. Completely destroy them—the Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusites—as the Lord your God has commanded you. Otherwise, they will teach you to follow all the detestable things they do in worshiping their gods, and you will sin against the Lord your God.(Deut. 20: 10-18)
- Muhammad ibn Saad. Kitab al-Tabaqat al-Kabir vol. 3. Translated by Bewley, A. (2013). The Companions of Badr. London: Ta-Ha Publishers.
- Ibn Hisham , Ibn Ishaq, Alfred Guillaume (translator) (1998). The life of Muhammad: a translation of Isḥāq's Sīrat rasūl Allāh (PDF). Oxford University Press. p. 201.
- Sahih al-Bukhari, 5:59:286
- Ibn Ishaq, (Collected by Shaykh Safiur Rahman Al Mubarakpuri). Tafsir Ibn Kathir (Volume 3). Darussalam. p. 145. ISBN 9789960892740. Retrieved Jan 19, 2015.
- Sahih al-Bukhari, 5:59:378
- "Mubarakpuri, The Sealed Nectar, Chapter Al-Ahzab Invasion
- A Life of Mahomet and History of Islam to the Era of the Hegira, volume 3, page.
- Mohammed Abu-Nimer (2000–2001). "A Framework for Nonviolence and Peacebuilding in Islam". Journal of Law and Religion. 15 (1–2): 247. doi:10.2307/1051519.
- Hashmi, Sohail H.; Buchanan, Allen E; Moore, Margaret (2003). States, Nations, and Borders: The Ethics of Making Boundaries. Cambridge University Press.
- Khadduri, Majid (1955). War And Peace in the Law of Islam. Baltimore: Johns Hopkins Press.
- Bassam Zawadi, "The Execution of The Jews At Bani Quraydah", Call To Monotheism, accessed 9 May 2017.
- Ahmad, Mirza Bashiruddin Mahmud. LIFE OF MUHAMMAD (PDF). pp. 100–101. ISBN 978-1853720451. Retrieved Jan 20, 2015.
- Sahih al-Bukhari, 5:58:148
- Sahih al-Bukhari, 5:58:147
- Sahih al-Bukhari, 5:58:146