Psalm 51 is a prayer of repentance. David prayed this prayer when the prophet Nathan went to him, after he had gone into Bathsheba.

Have mercy upon me, O God,
According to Your loving-kindness;
According to the multitude of Your tender mercies,
Blot out my transgressions.
² Wash me thoroughly from my iniquity,
And cleanse me from my sin.

³ For I acknowledge my transgressions,
And my sin is always before me.
⁴ Against You, You only, have I sinned,
And done this evil in Your sight—
That You may be found just when You speak,
And blameless when You judge.

⁵ Behold, I was brought forth in iniquity,
And in sin my mother conceived me.
⁶ Behold, You desire truth in the inward parts,
And in the hidden part You will make me to know wisdom.

⁷ Purge me with hyssop, and I shall be clean;
Wash me, and I shall be whiter than snow.
⁸ Make me hear joy and gladness,
That the bones You have broken may rejoice.
⁹ Hide Your face from my sins,
And blot out all my iniquities.

¹⁰ Create in me a clean heart, O God,
And renew a steadfast spirit within me.
¹¹ Do not cast me away from Your presence,
And do not take Your Holy Spirit from me.

¹² Restore to me the joy of Your salvation,
And uphold me by Your generous Spirit.
¹³ Then I will teach transgressors Your ways,
And sinners shall be converted to You.

¹⁴ Deliver me from the guilt of bloodshed, O God,
The God of my salvation,
And my tongue shall sing aloud of Your righteousness.
¹⁵ O Lord, open my lips,
And my mouth shall show forth Your praise.
¹⁶ For You do not desire sacrifice, or else I would give it;
You do not delight in burnt offering.
¹⁷ The sacrifices of God are a broken spirit,
A broken and a contrite heart—
These, O God, You will not despise.

¹⁸ Do good in Your good pleasure to Zion;
Build the walls of Jerusalem.
¹⁹ Then You shall be pleased with the sacrifices of righteousness,
With burnt offering and whole burnt offering;
Then they shall offer bulls on Your altar.