Sayyiduna Thabit bin al-Dahhak (may Allah be pleased with him), who was one of the people of the Tree, narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever swears by a religion other than Islam, he is as he said; and there is no vow upon the son of Adam in what he does not own; and whoever kills himself with something in this world will be punished with it on the Day of Resurrection; and whoever curses a believer, it is like killing him; and whoever accuses a believer of disbelief, it is like killing him."
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1324