Musannaf Ibn Abi Shaybah 39392 — Reports on the letters of the Prophet

It is narrated from Sayyiduna Usamah (may Allah be pleased with him): The Messenger of Allah (peace and blessings be upon him) sent us out on a military expedition, and we attacked al-Huraqat of the tribe of Juhaynah in the morning. I overtook a man, and he said: La ilaha illa Allah (There is no god but Allah). I stabbed him with a spear. Then this settled heavily in my heart, so I mentioned it to the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said: He said La ilaha illa Allah and you still killed him? The narrator said: I said: O Messenger of Allah (peace and blessings be upon him), he only said this word out of fear of weapons. He (peace and blessings be upon him) said: Why did you not split open his heart, so that you would have known whether he said this word out of fear of weapons or not? He (peace and blessings be upon him) repeated this so many times that the wish arose in my heart that (if only) I had accepted Islam that very day.