If you his issue is with Hadith, consider showing him Quran-alone resources. r/Quraniyoon is a good place on that sort of thing. Maybe his issue is with the fact that he believes Muslims revere the Prophet Muhammad to the extent that they do God, as the Christians do with Isa. Maybe showing him an angle of Islam that is more dubious and critical of the transmission of Hadith literature will be more inviting to him. I consider myself part of this group, and although I still believe Muhammad to be the messenger of Islam, I find that more Quran-centric Muslims are less prone to holding Hadith and the idealism of Muhammad being akin to God than other sects may be prone to.