عَنْ أُسَامَةَ بْنِ زَيْدٍ قَالَ بَعَثَنَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ إِلَى الْحُرَقَةِ مِنْ جُهَيْنَةَ قَالَ فَصَبَّحْنَاهُمْ فَقَاتَلْنَاهُمْ فَكَانَ مِنْهُمْ رَجُلٌ إِذَا أَقْبَلَ الْقَوْمُ كَانَ مِنْ أَشَدِّهِمْ عَلَيْنَا وَإِذَا أَدْبَرُوا كَانَ حَامِيَتَهُمْ قَالَ فَغَشِيتُهُ أَنَا وَرَجُلٌ مِنَ الْأَنْصَارِ قَالَ فَلَمَّا غَشِينَاهُ قَالَ لَا إِلَهَ إِلَّا اللَّهُ فَكَفَّ عَنْهُ الْأَنْصَارِيُّ وَقَتَلْتُهُ فَبَلَغَ ذَلِكَ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ فَقَالَ يَا أُسَامَةُ أَقَتَلْتَهُ بَعْدَ مَا قَالَ لَا إِلَهَ إِلَّا اللَّهُ قَالَ قُلْتُ يَا رَسُولَ اللَّهِ إِنَّمَا كَانَ مُتَعَوِّذًا مِنَ الْقَتْلِ فَكَرَّرَهَا عَلَيَّ حَتَّى تَمَنَّيْتُ أَنِّي لَمْ أَكُنْ أَسْلَمْتُ إِلَّا يَوْمَئِذٍ
It is narrated from Sayyiduna Usama bin Zaid (may Allah be pleased with him), he says: The Messenger of Allah (peace and blessings be upon him) sent us towards the tribe of Harqa from Banu Juhaina. We reached them early in the morning and fought with them. Among them was a man who, whenever his people came forward to fight, he fought bravely, and when they turned their backs and fled, he defended them. I and an Ansari overpowered him. When we had subdued him, he recited "La ilaha illallah" (There is no god but Allah). The Ansari (may Allah be pleased with him) withheld his hand from killing him, but I killed him. When this matter reached the Noble Prophet (peace and blessings be upon him), he said: O Usama! Did you kill him even after he had recited the Kalimah? I said: O Messenger of Allah! He did not recite the Kalimah from his heart; he only recited it to save his life. But (to refute me) the Prophet (peace and blessings be upon him) repeated his statement so much that I wished I had not accepted Islam before this, but had become a Muslim today (so that this mistake would not have occurred from me, or it would have been forgiven due to the acceptance of Islam).