- What is the ruling on praying behind an Imam for whom one harbors hatred or resentment? - What is the ruling on saying "You are one of the disbelievers of Quraish" to a colleague in a serious, non-joking conversation?

Prayer is valid behind an Imam whom the worshiper dislikes for some reason. It is preferable to struggle against one's soul to remove hatred and animosity towards him if it is a personal feeling. Saying "You are one of the disbelievers of Quraish" with the intention of declaring someone an infidel is a grave sin, and the one who says it must repent.