Sayyiduna Thabit bin Dhahak (may Allah be pleased with him) was among the Companions of the Tree (those who pledged allegiance at Ridwan). He narrated that the Messenger of Allah (peace and blessings be upon him) said: Whoever swears by a religion other than Islam (saying, "If I do such-and-such, then I am a Christian, a Jew"), then he will become as he said. And a vow is not valid for a person regarding things that are not within his control. And whoever commits suicide with anything in this world will be punished with that same thing in the Hereafter. And whoever curses a Muslim, it is as if he has shed his blood, and whoever calls a Muslim a disbeliever, it is as if he has killed him.