The Ruling on the Worship of One Who Drinks Alcohol

Question :

If a person drinks alcohol, always commits illegal sexual intercourse, and he performs the prayer and all of the other pillars (of Islam), but he does not abandon drinking alcohol or illegal sexual intercourse, are his acts of worship valid?

Answer:

Whoever drinks alcohol and commits illegal sexual intercourse or any other sin and declares it to be permissible, then he is guilty of disbelief. No action is accepted when accompanied by disbelief. Whoever commits a sin and he accepts the fact that it is forbidden, but is overcome by his self, and he asks Allah to protect him from it, he is a believer due to faith and a sinner due to his sin.

It is incumbent upon the worshipper, when he commits any sin, to repent and return to Allah, the All-Powerful, Most High, acknowledge his sin, resolve firmly not to return to it, to regret what he has done, not to play with Allah's religion, and not to be misled by Allah's protection of him and granting him a respite.

This is because Allah, the All-Powerful, Most High expelled Iblis from His Mercy and banished him permanently and called him the accursed Satan because of one sin: Allah commanded him to prostrate to Adam, peace be upon him, and he refused. So Allah sent Adam, peace be upon him, down from Paradise because he disobeyed Allah, the All-Powerful, Most High once. But Adam, peace be upon him, repented, then Allah forgave him and guided him to the Straight Path. So it is not permissible for the worshipper to behave with the behavior of a cunning deceiver towards his Lord. Rather, it is incumbent upon him to revere Allah as one who fears (Him), doing what He commands him to do and leaving what He prohibits for him.

Source:
The Permanent Committee
Fatawa Islamiyah, Vol. 6 Pages 207-208