He participated in the battle against Musaylimah as a standard bearer of the Muhajireen and displayed unexpected valour. His people feared that he would show weakness or be too terrified to fight. To them he said, "If you manage to overtake me, what a miserable bearer of the Qur'an I shall be." He then valiantly plunged into the enemy ranks and eventually died in battle.
When Umar was dying, he was questioned about his successor, and he said: ‘If Abu Obaida bin al-Jarrah were alive, I would have made him the khalifa. If Khalid bin al-Walid were alive, I would have appointed him the amir of the Muslims. And if Salim, the client of Abu Hudhaifa, were living today, then I would have designated him as your ruler.' This Salim was a slave who came from Istakhr in Persia. He was emancipated, and became a ‘mawali' (client) of Abu Hudhaifa. He was well-known for his piety. Many Muslims deferred to him in matters of Faith even in the times of the prophet Muhammad. Sometimes he led the Muslims in prayer also. He was killed in the Ridda wars during the khilafat of Abu Bakr. He was a devout and God-fearing man.
It was really unfortunate for the Umma that Salim was dead or else Umar would have made him his successor, and he might have made an excellent khalifa. At any rate, Umar knocked down that “tradition” of the Apostle which Abu Bakr had quoted before the Ansar in Saqifa according to which no one but the Quraysh had the right to become rulers. Here was Umar, the greatest “pontiff” of the Sunni establishment, ready, willing and eager to make Salim,the khalifa of the Muslims, who was:
a ‘non-free' man, a client, a man who was emancipated by an Arab, and who was under his protection.
Umar “proved” on his deathbed that the “tradition” of the “Qurayshi connection” by which the Muhajireen had claimed their “superiority” over the Ansar in Saqifa, was spurious, and he “proved” that to be a khalifa of the Muslims, it was not necessary to be a Qurayshi after all. Umar could consider a former slave who was not distinguished for anything except for his piety, for the most important position in Islam but he could not consider an Ansari for it, even if he had distinguished himself in war and peace.
He had contributed in all major battles, such as Badr, Uhud, Ahzab etc., so he is a Badrian Companion of Muhammad.