Uqba bin Malik reported,

A military expedition sent out by the Messenger of Allah ﷺ attacked a tribe at their watering place in the early morning. A man from among them came forward, and a Muslim charged at him. The man cried out, "I am a Muslim," but the Muslim killed him anyway.When they returned, they informed the Prophet ﷺ of what had happened. The Messenger of Allah ﷺ stood up to address the people. He praised Allah and glorified Him, then said, "What is the matter with a Muslim who kills a man even as the man declares, 'I am a Muslim'?"The man who had done the killing said, "He only said it seeking protection."The Messenger of Allah ﷺ turned his face away, extended his right hand, and said, "Allah refuses to accept from me anyone who kills a Muslim," repeating it three times.

Ahmad 17009

Sahih

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 ﷺ غشوا أهل ماء صبحا فبرز رجل من أهل الماء فحمل عليه رجل من المسلمين فقال إني مسلم فقتله فلما قدموا أخبروا النبي ﷺ بذلك فقام رسول الله ﷺ 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 ﷺ وجهه ومد يده اليمنى فقال أبى الله علي من قتل مسلما ثلاث مرات

أحمد 17009صحيح
Contents
Reference
Commentary
Ayat
Collection
Musnad Ahmad
Book
Uqba bin Malik
Numbering
Darussalam 17009
Ahmad 17009