Nishmat (נִשְׁמַת or Nishmat Kol Chai, The breath of every living thing) is a Jewish prayer that is recited following the Song of the Sea during Pesukei D'Zimrah but before Yishtabach on Shabbat and Yom Tov. It is also recited during the Passover seder in some traditions. The recitation of this prayer is not required by halakha in Judaism, but nevertheless, is prized by halakhic authorities because the concepts covered in this prayer are basic to Halakha.
In this prayer, the word Nishmat (the combining form of Nishmah נִשְׁמָה breath) that begins the prayer is related to the word neshama (נְשָׁמָה soul), suggesting that the soul is part of the breath of all life. The theme of the prayer is the uniqueness of God.
Some hold that answers to certain issues of Jewish law (halakha) can be derived from the prayer Nishmat. The commandment Do not lie idly by the blood of your neighbor requires a person to rescue another s/he sees is in danger. But from Nishmat, it can be seen that one who is not physically present where the danger is taking place is exempt from performing any rescue action. Some examples of this include the obligation to rescue a person from a burning building in one's own location, but an exemption from the obligation to donate an organ when doing so can save a life (though doing so is still permitted).
Nishmat is considered one of the masterpieces of Jewish liturgy. It is seen as a journey of self-discovery, describing God as a source of prayer.
The composition date of this prayer is believed to have be from the Amoraic era or earlier. In the Talmud (Bavli Pesahim 118a), Rabbi Yochanan bar Nafcha (180-279 CE), states that this prayer should be recited during the Passover Seder after Hallel. This has been current practice at least since the Geonic period (c. 800-1000 CE). While this is the earliest known reference to the prayer, there are opinions that it may be older.
Nishmat became a standard part of the liturgy by the time of Saadia Gaon. The earliest mention of it as part of the Sabbath morning service is in Seder Rav Amram written by Rav Amram Gaon in the ninth century CE. In Mishneh Torah, Maimonides (12th century CE) states that it was recited on the Sabbath in Sephardic practice. Its use on Sabbath morning was controversial in Europe during the early medieval period. Several Ashkenazic rabbinic works explicitly defended its use, including Mahzor Vitry and Kol Bo.
The exact author of the prayer is not known. Some scholars have suggested that it was authored by a man named Yitzchak (יצחק, Isaac) with a wife named Rivka (רבקה, Rebecca) based on the acrostic arrangement of the verses, but others have dismissed this idea.
Some scholars have suggested that the author's name may have been Shimon (שמעון, Simon) from an acrostic within the prayer, and have considered this could be Shimon ben Shetach or perhaps even (according to some Messianic/Christian ideas) the Apostle Peter, whose Hebrew name was Shimon, which would place the date of authorship in the first century C.E. 
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