The text comes from Ps. 129 (130):1-2: De profundis clamavi ad te, Domine; Domine, exaudi vocem meam. Fiant aures tuae intendentes in vocem deprecationis meae. (Out of the depths I have cried to thee, O Lord: Lord, hear my voice). This beautiful rendition of the Gregorian De profundis is sung by the Nova Schola Gregoriana and conducted by Alberto Turco.
Image: illuminated page of the first psalm ("Beatus Vir") in the Howard Psalter (c. 1310-1320).