Is it permissible for me to atone for a sin committed by my father, who is now deceased?

Among the greatest acts of filial piety towards parents are frequent seeking of forgiveness (istighfar) and supplication (dua) for them, giving charity on their behalf, and fulfilling any outstanding obligations they may have, such as zakat (definition) and expiations (kaffarat). It is also permissible to perform Hajj on their behalf. Many scholars hold the view that it is permissible to perform good deeds and dedicate their reward to them. If the sin necessitates an expiation, then fulfilling it benefits them. However, if it was a sin that can only be expiated by repentance, and they did not repent from it, then their matter is left to the will of Allah, and they do not benefit from the repentance of others.