- Go and look for some sahih, strong hadith, which are clearly silly, and show him. Perhaps he will agree.
- You cannot and should not try to convince others. You may share your stance and give your reasons, but don't do it with the agenda to convince him. Don't try to change someone else. Just be a role model.
Words of Wisdom, right there!
I actually lost a friend over this and I was not trying to convince him, he was trying to convince me. I asked him about a hadith that applied to his personal situation and he replied that it was not known if that hadith was authentic. So I asked how HE PERSONALLY decided which hadith he considered authentic and he actually said he wasn't too well versed on hadith. So... these things that he admittedly does not know much about, he is insisting I govern my life by. I asked that and have not talked to him since. He pretty much told me I was naive and hung up angry. Eh, wtvr, ya know.
I've kinda learned it is best to submit to Allah(swt) the way you truly believe you should and let others do the same.