Nishmat at Night

Can I say nishmat kol chai in the evening?

Shalom!

Thank you for your question.

For the benefit of all readers, allow me to begin with a small overview of the Nishmat prayer.

Nishmat is a very old prayer that was composed sometime in the Talmudic era. Indeed, it is mentioned in the Talmud where we find, Rabbi Yochanan bar Nafcha instituting it as part of the Passover Seder along with the Hallel prayer.

The exact author of Nishmat is unknown, and it might actually be the result of multiple authors as it appears that the passage of "If our mouths were as full of song as the sea...we could not sufficiently praise You O Lord our God" is likely taken from the words of Rabbi Yochanan. The opening words of Nishmat ("the soul of every living thing"), as well as the term "Creator of all souls" seems to be taken from Tehillim 150:6.

Nishmat became a standard part of the prayer service in the time of the Geonim as it is included in the famous siddur of Rav Amram Gaon with Maimonides, the Rambam, specifically singling it out as a prayer recited on Shabbat, a practice which continues until tis day.

That bring said, although Nishmat is generally reserved for Shabbat and holidays, and is recited as part of the preliminary Pesukei D’zimra section, there is nothing wrong with reciting it at night if one feels the need to do so, such as to express thanksgiving to G-d for a certain good event or good fortune.

Berachot 59b, Pesachim 118a