1 Der du bist drei in Einigkeit,ein wahrer Gott von Ewigkeit,die Sonn mit dem Tag von uns weicht,laß leuchten uns dein göttlich Licht.2 Des Morgens, Gott, dich loben wir,des Abends auch beten vor dir,unser armes Lied rühmet dichjetzund, immer und ewiglich.3 Gott Vater dem sei ewig Ehr,Gott Sohn der ist der einig Herr,und dem Tröster Heiligen Geist,von nun an bis in Ewigkeit.Dr. M. Luther, 1543.(Nach dem Lateinischen des heil. Ambrosius.)
My prose translation:
1 You Who are three in unity,A true God from eternity,The sun with the day is leaving us,Let Your divine light shine for us.2 In the morning, God, we praise You;In the evening, too, [we] pray to You;Our poor song extols YouNow, always, and eternally.3 To God the Father be glory eternally,To God the Son, Who is the only Lord,And to the Comforter, [the] Holy Ghost,From now on unto eternity.Dr. M. Luther, 1543.(After the Latin of the holy Ambrosius.)
As far as I can tell, this hymn isn't in The Lutheran Hymnal, Lutheran Worship, or The Lutheran Service Book. According to the Gesangbuch, the text is sung to "its own tune." There are two arrangements of "Der du bist Drey in Einigkeit" in Telemann's Fast allgemeines Evangelisch-Musicalisches Lieder-Buch, although there seem to be more notes than there are words in the above text, so I don't know if this is the same tune that the Gesangbuch indicates.