Is it obligatory to leave a gathering where people are smoking, knowing that some students of knowledge do not leave it?

It is not permissible to sit with a smoker while he is smoking, except out of a need or a considerable benefit, while also condemning his action according to one's ability. Students of knowledge may have an excuse or see a preponderant benefit in doing so, and this does not contradict the impermissibility of smoking and the obligation to condemn it when able.