Dua to say during the last ten nights

The last ten nights of Ramadan is a major time to ask forgiveness.

Hadith Qudsi,

Allah said:O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind.O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you.O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great at it.- Saheeh. Related by at-Tirmidhi.

A dua'

ALLAAHUMMA INNAKA 'AFFUWWUN TUHIBB AL- 'AFWA FA 'AFFU 'ANNI

(O Allaah, You are Forgiving and You love forgiveness, so forgive me)

(Tirmidhi)