My questions is does his sins will be forgiven or he has to go through the punishment. If not what he should do to seek Allah’s forgiveness?
You state that the person has repented and become pious. His subsequent piety and change in life is a sign of his sincere repentance. Allah Ta’ala states in the noble Qur’aan, ?Oh my slaves who have oppressed themselves (by committing sins), do not be despondent of the mercy of Allah. Verily, Allah forgives all sins. Verily, Allah is Forgiving and Merciful.?
Rasulullah [sallallaahu alayhi wasallam] said, ?A Taaib (repenter) from sins is like he who never committed sins.? In another Hadith, Rasulullah [sallallaahu alayhi wasallam] said, ?a Taaib (repenter) is the beloved of Allah. If a person repents sincerely, Allah will forgive the person and not punish him.?
The person should be steadfast in his deeds of piety and never revert to the life of sins, Zina, alcohol, etc. He should also abstain from anything that will lead him to such sins.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai