Psalm 51:1

Have mercy on me, O God, according to your unfailing love; according to your great compassion blot out my transgressions. 

Have mercy on me, O God 
2 Samuel 24:14  David said to Gad (the prophet, David's seer), "I am in deep distress. Let us fall into the hands of the LORD, for his mercy is great; but do not let me fall into human hands."
Psalm 9:13  LORD, see how my enemies persecute me! Have mercy and lift me up from the gates of death, ...

according to your unfailing love 
Psalm 25:7  Do not remember the sins of my youth and my rebellious ways; according to your love remember me, for you, LORD, are good.
Psalm 119:88  In your unfailing love preserve my life, that I may obey the statutes of your mouth.

according to your great compassion 
Nehemiah 9:27  "So you delivered them into the hands of their enemies, who oppressed them. But when they were oppressed they cried out to you. From heaven you heard them, and in your great compassion you gave them deliverers, who rescued them from the hand of their enemies."
Psalm 86:15  But you, Lord, are a compassionate and gracious God, slow to anger, abounding in love and faithfulness.
Isaiah 63:7  I will tell of the kindnesses of the LORD, the deeds for which he is to be praised, according to all the LORD has done for us--yes, the many good things he has done for Israel, according to his compassion and many kindnesses.

blot out 
2 Samuel 12:13-14  Then David said to Nathan (the prophet), "I have sinned against the LORD." Nathan replied, "The LORD has taken away your sin. You are not going to die. But because  by doing this you have shown utter contempt for the LORD, the son born to you will die."
2 Chronicles 6:21  "Hear the supplications of your servant and of your people Israel when they pray toward this place. Hear from heaven, your dwelling place; and when you hear, forgive."
Nehemiah 4:4-5  Hear us, our God, for we are despised. Turn their insults back on their own heads. Give them over as plunder in a land of captivity. Do not cover up their guilt or blot out their sins from your sight, for they have thrown insults in the face of the builders.
Acts 3:19  "Repent, then, and turn to God, so that your sins may be wiped out, that times of refreshing may come from the Lord, ..."

my transgressions 
Psalm 39:8  Save me from all my transgressions; do not make me the scorn of fools.

(parentheses are mine)

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984, 2011 by Biblica, Inc.® Used by permission. All rights reserved worldwide. 
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