Q: Is it kufr (disbelief) to say to a Muslim that he is going to hell? If you know that a person is committing a major sin and you tell him ‘You are going to hell”, will this be kufr?
A: To tell someone that he is going to hell is a major sin. Repent from this. The most that could have been said is that his action is such that can lead to hell, but he cannot be told that he will go to hell. Also, when advising someone, advise with wisdom, kindness and compassion.
Moulana Yusuf Laher