Sayyiduna Usama bin Zaid (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) sent us to the branch of the tribe of Juhaina called Harqa. We attacked them in the morning and defeated them. The narrator says: I and an Ansari came upon one of their men. When we overpowered him, he said: "La ilaha illallah" (There is no god but Allah). The Ansari held back his hand, but I struck him with my spear and killed him. When we returned, the Prophet Muhammad (peace and blessings be upon him) had already been informed of this. The Prophet (peace and blessings be upon him) asked: "O Usama, did you kill him after he had said 'La ilaha illallah'?" Sayyiduna Usama (may Allah be pleased with him) narrates: I said, "O Messenger of Allah (peace and blessings be upon him)! He only said it to save his life." The Prophet (peace and blessings be upon him) asked: "Did you strike him with your spear after he had said 'La ilaha illallah'?" After that, the Prophet (peace and blessings be upon him) kept repeating this statement until I wished that I had not accepted Islam before that day.