My seventy-year old father drinks alcohol and tries to conceal this. What is my duty towards him? Also, he does not pray regularly except for the Friday prayer (Jumu`ah). What is the best way to advise him?
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.
You have to advise your father and explain to him how drinking alcohol is one of the gravest sins. In doing so, you have to choose the best way of giving such advice. You also have to advise him, in the same manner, that failure to perform obligatory prayers is an act of disbelief. You should support all of your advice with authentic proof from the Quran and the Sunnah.
You are probably the best person to answer your own question regarding the best way to advise your father. If your direct advice has an impact on him because he appreciates you and your dutifulness towards him, then this would undoubtedly be better and more effective. Otherwise, seek help from people he trusts and listens to, such as pious scholars, relatives or friends. You can also use audio lectures and sermons.
Allaah Knows best.
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