All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is absolutely no doubt that drinking alcohol is a grave and major sin that entails the prescribed corporal punishment in the worldly life and severe punishment in the Hereafter if the person dies without repenting of it. It is enough to warn people against drinking alcohol to mention the saying of the prophet, sallallaahu ‘alayhi wa sallam: "Every kind of intoxicants is haram, and Allaah has set a pledge (vow) upon Himself that He will force those who drink intoxicants (wine and its like) to drink from 'Teenat Al-Khabaal'." It was said: "O Messenger of Allaah! What is Teenat Al-Khabal?" He answered: "It is made of the sweat and pus of the dwellers of Hell." [Muslim]
It is incumbent upon the one who is afflicted with drinking alcohol to repent to Allaah Almighty, sincerely and truthfully, and to not go back to drinking it. Let them contemplate the saying of Allaah Almighty (which means): {O you who have believed, indeed, intoxicants, gambling, [sacrificing on] stone alters [to other than Allaah], and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful. Satan only wants to cause between you animosity and hatred through intoxicants and gambling and to avert you from the remembrance of Allaah and from prayer. So will you not desist?} [Quran 5: 90-91]
In this verse, Allaah Almighty starts by mentioning alcohol. He, the Exalted, mentioned it before gambling, sacrificing on stone alters to other than Allaah, and divining arrows because of the destructive effects this has on the individual and the society. Drinking alcohol has always been the reason behind many crimes and disasters and causes adultery, murder, theft and the like of those destructive crimes. It is unquestionably the mother of all evils. The fact that the person in question observes the obligatory acts of worship such as prayer, fasting and charity and, in spite of all that, he goes on drinking alcohol is really something problematic. It is incumbent upon you to remind him of Allaah Almighty, encourage him to repent, and do not let him lose hope in the Mercy of Allaah Almighty. Explain to him that he has to adopt the ways that lead to repentance and never neglect prayer nor other obligatory acts of worship. Rather, he has to make his prayer and worship a means to get rid of drinking alcohol since Allaah Almighty says (what means): {Indeed, prayer prohibits immorality and wrongdoing.} [Quran 29: 45]
Another factor that helps the person to repent is to have good companions and keep away from evil ones, learn good knowledge, think about the ends of matters, and supplicate Allaah Almighty to be freed from this sin, along with changing the surrounding environment and searching for a good one.
Allaah Knows best.