Old Testament readings use the Septuagint , the Scripture the apostles quoted. Masoretic numbering shown for reference.Learn why
LXX2012

Psalms 50:1

(51) For the end, a Psalm of David, when Nathan the prophet came to him, when he had gone to Bersabee. Have mercy upon me, O God, according to your great mercy; and according to the multitude of your compassions blot out my transgression.

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