Here's a YouTube video of this Introit, sung by "the three cantores of the major seminary of the diocese of Haarlem (The Netherlands)":
The text comes from verses 1-4 of Psalm 25, Ad te, Domine, levavi:
1 To You, O LORD, I lift up my soul.
2 O my God, I trust in You;
Let me not be ashamed;
Let not my enemies triumph over me.
3 Indeed, let no one who waits on You be ashamed;
Let those be ashamed who deal treacherously without cause.
4 Show me Your ways, O LORD;
Teach me Your paths.