Narrated Usama bin Zaid: Allah's Apostle sent us towards Al-Huruqa, and in the morning we attacked them and defeated them. I and an Ansari man followed a man from among them and when we took him over, he said, La ilaha illal-Lah. On hearing that, the Ansari man stopped, but I killed him by stabbing him with my spear. When we returned, the Prophet came to know about that and he said, O Usama! Did you kill him after he had said La ilaha ilal-Lah? I said, But he said so only to save himself. The Prophet kept on repeating that so often that I wished I had not embraced Islam before that day.