Hadith 451:3
Yunus narrated to us, Hammad—meaning Ibn Salamah—narrated to us, from Yunus ibn Ubayd, from Humayd ibn Hilal, who said: A man brought me and Bishr ibn Asim together, and he narrated to me from Uqbah ibn Malik that a detachment of the Messenger of Allah (peace and blessings of Allah be upon him) raided the people of a watering place in the morning. A man from the people of the watering place came out, and a man from the Muslims attacked him. He said, "I am a Muslim," but he killed him. When they arrived, they informed the Prophet (peace and blessings of Allah be upon him) of that. The Messenger of Allah (peace and blessings of Allah be upon him) stood up to deliver a sermon, praised Allah and extolled Him, then said: "As for what follows, what is the matter with a Muslim who kills a man while he is saying, 'I am a Muslim'?" The man said, "He only said it to seek refuge." The Messenger of Allah (peace and blessings of Allah be upon him) turned his face away and extended his right hand, saying: "Allah has refused me [to accept the excuse of] one who kills a Muslim," three times.
حدثنا يونس، حدثنا حماد يعني ابن سلمة، عن يونس بن عبيد، عن حميد بن هلال، قال: جمع بيني وبين بشر بن عاصم، رجل فحدثني عن عقبة بن مالك، أن سرية لرسول الله صلى الله عليه وسلم غشوا أهل ماء صبحا، فبرز رجل من أهل الماء، فحمل عليه رجل من المسلمين، فقال: إني مسلم فقتله، فلما قدموا أخبروا النبي صلى الله عليه وسلم بذلك، فقام رسول الله صلى الله عليه وسلم خطيبا، فحمد الله وأثنى عليه، ثم قال: " أما بعد، فما بال المسلم يقتل الرجل وهو يقول: إني مسلم "، فقال الرجل: إنما قالها متعوذا، فصرف رسول الله صلى الله عليه وسلم وجهه، ومد يده اليمنى، فقال: " أبى الله علي من قتل مسلما " ثلاث مرات