Usama reported, "The Messenger of Allah ﷺ sent us on an expedition to al-Huraqah. We attacked the people at dawn and defeated them. A man from the Ansar and I caught up with one of their men, and when we overtook him, he said, 'There is no god but Allah.' The Ansari held back from him, but I stabbed him with my spear and killed him.When we returned, news of this reached the Prophet ﷺ, who said, 'Usama, did you kill him after he said, There is no god but Allah?'I replied, 'He only said it to save himself.'He kept repeating the question to me until I wished I had not embraced Islam before that day."
بعثنا رسول ﷺ إلى الحرقة، فصبحنا القوم فهزمناهم، ولحقت أنا ورجل من الأنصار رجلا منهم فلما غشيناه قال: لا إله إلا الله. فكف عنه الأنصاري، فطعنته برمحي حتى قتلته، فلما قدمنا بلغ ذلك النبي ﷺ فقال: يا أسامة، أقتلته بعد ما قال: لا إله إلا الله قلت: كان متعوذا! فما زال يكررها حتى تمنيت أني لم أكن أسلمت قبل ذلك اليوم.
Bukhari reported it in the Book of Campaigns (4269), and Muslim in the Book of Faith (159:96), both of them through Hushaym, who said, Husayn informed us, Abu Dhubyan narrated to us, he said, I heard Usama bin Zayd bin Haritha narrating, he said, and he mentioned it.