My Father's Struggle with Hashish and His Faith

Assalamu alaikum, everyone. I recently discovered that my father uses hashish, and it's really weighing on me. I wasn't meant to find out the way I did-I came across it while looking through his phone. Now I'm confused and don't know what to do. He is so consistent with his Salah, never missing his five daily prayers, and he's always giving Sadaqah and helping others. But this habit... it's really conflicting for me. I want to approach him with respect and concern, but I'm unsure how to start that conversation without causing hurt or disrespect. Any advice from those who may have been in a similar situation would be appreciated. Jazakum Allahu khairan.