Assalamu Alaykum WR WBMy grandparents are divorced and I had learned that my grandfather cheated on my grandmother. I ended up making some badua and now I regret it so much. I just want to know if there is something besides my askings for forgiveness that should be done. I really regret it and I feel so guilty when ever I see him. I would also like to make dua to Allah to forgive him as well because of his mistake(s). He has health issues but is active Alhamdulillah. Please help me and Allah bless you all.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

We do not know what you exactly meant by saying that your grandfather “cheated your grandmother”. However, if he had established emotional relationships with other women, for example, then there is no doubt that he is wrong and sinful.

Allah has forbidden taking lovers (or girlfriends) as He Says (what means): {….desiring chastity, not unlawful sexual intercourse or taking [secret] lovers.} [Quran 5:5]

However, this does not justify for you to supplicate against him, as there is a religious text which prohibits supplicating against a sinful Muslim. Abu Hurayrah narrated: "A man who had drunk wine was brought to the Prophet and he asked us to beat him; some struck him with their hands, some with their garments (making a whip) and some with their sandals. When he (the drunkard) left, some of the people said: ‘May Allah disgrace you!’ Thereupon, the Prophet said, ‘Do not say so. Do not help the devil against him.'" [Al-Bukhaari]

Hence, you have to repent, and supplicate for your grandfather as the Prophet supplicated: "O Allah, Muhammad is a human being. I lose my temper just as human beings lose their temper, and I have held a covenant with You which You wouldn’t break: For any believer whom I harmed, insulted, or lashed, make that an expiation (of his sins and a source of) his nearness to You on the Day of Resurrection." [Muslim]

Allah knows best.