Let the man make his own decision on this matter. Don't sermon.
It is best they get fully committed and well-cocooned to something and get burned on it in the end by their own hand....so they have no recourse to blame the evil Indian society for that (though some like afrazul are so long gone for even that to work).
You need leave some people to be, and observe the "new buds" they hang out with and like and support and quote. But its important you give enough time for this...a year or two...to see what waxes and wanes among that crew more naturally and instrinsically....it can be enough to do the job by itself, dependent on the character and specifically his own honesty, upbringing and distaste to hypocrisy....i.e root character.
Then (and only if really needed) you go for final jugular at the end, there is lot of material from this "new buddy" lot (down to exact same members even) they have spewed from years before when they were far more honest and open about their thoughts and intentions to indian muslims (far more than the naive or desperate "new" indian muslim members here can imagine...you have to dig deep and compile it and provide the sobering context too).
There is time and place to show that hand, now is not the time....now is the time to let everything keep proceeding here as is...and let natural course of lessons take it shape.