A:
You were right when you advised this fellow Muslim of yours to continue offering Salah in congregation regardless of the sins he may commit. This is because minor sins like gazing at women are forgiven by offering the five daily prayers, attending the Friday Prayer and seeking Allah's forgiveness. As for major sins like theft and adultery, they are forgiven by offering sincere repentance to Allah. (Part No. 7; Page No. 300) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.