Looks like the father knows the consequences of his son's action and he just wants to guide him no matter what the scenario is, we don't appreciate this kind of love from our parents until they are no longer here with us and by that time we realize that no one has ever been truthful to us except them. He should always listen to his father and learn to be contented in his life since they all have the means to survive. If he accepted it, I'm sure it won't be the last time the son does it and until the whole family is addicted to it.
I think the father didn't like the idea of money coming into his life through his son's gambling, especially if he holds strong religious and Islamic beliefs. Easy money obtained through luck might be something he wishes to avoid in his household. Additionally it could be a wise decision to prevent any potential addiction issues from developing in his son's future as he becomes into gambling.
Personally, I have friends who are gamblers and have been losing alot, they are slowly falling into the trap of addiction, despite my efforts to advise them to reduce their gambling activities. Unfortunately, they don't seem to heed my advice. :/ but I'll keep trying with them to get off it.