The Arabic Letter Sad - 38:29
Blessed is this Book which We have sent down to you, that they may examine its verses and that those of understanding may take admonition.
To turn to Allah; to repent and ask for forgiveness:
The Table Spread/5:39
Whoever repents and reforms after this injustice, Allah will accept his return. Surely Allah is Forgiving, Merciful.
The Table Spread/5:74
Will they not turn to Allah and ask forgiveness from Him? Allah is Forgiving, Merciful.
The Repentance/9:117
Allah has accepted the repentance of the Messenger and those who emigrated and those who helped. They followed him at a time of difficulty when some of them almost lost heart. Then He accepted their turning (repentance). He is Most Compassionate towards them, Most Merciful.
The Prohibition/66:4
If you both repent to Allah, your hearts will be turned. And if you support one another against him (the Messenger), Allah is his guardian, and Jibril and the righteous believers and the angels support him.