Reference for Psalms 42:9

יוֹמָ֤ם ׀ יְצַוֶּ֬ה יְהוָ֨ה ׀ חַסְדּ֗וֹ וּ֭בַלַּיְלָה שירה [שִׁיר֣וֹ] עִמִּ֑י תְּ֝פִלָּ֗ה לְאֵ֣ל חַיָּֽי׃

By day the LORD will command His lovingkindness, and in the night His song shall be with me, even a prayer unto the God of my life.

ספר השרשים