What is the way to deal with the whisperings that bring to mind past sins after repentance, which cause sadness and pain and even affect prayer?

The pain a repentant person feels from remembering past sins is a sign of good and sincerity of repentance. They should rejoice in God's forgiveness and mercy, as Allah states: "And whoever does evil or wrongs himself then seeks forgiveness of Allah will find Allah Forgiving and Merciful." And His saying: "Your Lord has decreed upon Himself mercy. Indeed, anyone of you who does wrong out of ignorance and then repents after that and corrects himself - then indeed, He is Forgiving and Merciful." It is necessary to suppress the whispers of Satan that exaggerate the sin and to frequently contemplate the texts of hope. Therefore, strengthen hope when the enemy tries to cut off hope or when you feel lazy.