Question 9: What is the ruling on a person who drinks Khamr (intoxicants) at night and offers Salaah (Prayer) during the day? As Salaah should prevent a person from committing immoral acts and Munkar (that which is unacceptable or disapproved of by Islaamic law and Muslims of sound intellect), is their Salaah valid or not?
Answer: If a person offers Salaah with all its obligatory acts and fulfills its conditions, it is considered valid. They will be rewarded for it, and they will be sinful for drinking Khamr. They are considered among those who mix good deeds with evil ones… read more here.