668 — Ubayd Allah ibn Umar narrated to us: Hammād ibn Zayd narrated to us, on the authority of Ayyūb, on the authority of Abū Qilābah, on the authority of Thābit ibn al-Dahhāk, who was a Companion. Hammād said, “I would have no qualms about saying that it was traced back to the Prophet.” He said: “Cursing a believer is equivalent to killing him. Whoever calls him a disbeliever, it is as though he killed him. And whoever falsely swears by a religion other than Islam is as he has said.”