De Profundis means literally 'Out of the Depths' in Latin and is taken from the first line of Psalm 130.
In Rome, the "De Profundis" is rung every evening by the parish churches one hour after the Ave Maria. Clement XII in 1736 granted an indulgence for this practice and endeavored to extend it. This custom is observed in many other places, particularly in North America.
At 9 o'clock every evening, a nine-count slow toll is rung, one toll for each line of the prayer.
[Canticum graduum] De profundis clamavi ad te, Domine; Domine, exaudi vocem meam. Fiant aures tuæ intendentes in vocem deprecationis meæ. Si iniquitates observaveris, Domine, Domine, quis sustinebit? Quia apud te propitiatio est; et propter legem tuam sustinui te, Domine. Sustinuit anima mea in verbo ejus: Speravit anima mea in Domino. A custodia matutina usque ad noctem, speret Israël in Domino. Quia apud Dominum misericordia, et copiosa apud eum redemptio. Et ipse redimet Israël ex omnibus iniquitatibus ejus.
[A Song in steps] From the depths, I have cried out to you, O Lord; Lord, hear my voice. Let your ears be attentive to the voice of my supplication. If you, Lord, were to mark iniquities, who, O Lord, shall stand? For with you is forgiveness; and because of your law, I stood by you, Lord. My soul has stood by his word. My soul has hoped in the Lord. From the morning watch, even until night, let Israel hope in the Lord. For with the Lord there is mercy, and with him is plenteous redemption. And he will redeem Israel from all his iniquities.