Musnad Abu Ya'la al-Mawsili 172:1

Shayban ibn Farrukh narrated to us, Sulayman ibn al-Mughirah narrated to us, Humayd ibn Hilal narrated to us. He said: Abu al-Aliyah came to me and a companion of mine and said, "Come, for you two are younger in youth and more retentive of hadith than I." So we set out until we came to Bishr ibn Asim al-Laythi. Abu al-Aliyah said, "Narrate to these two a hadith." Bishr said: Uqbah ibn Malik al-Laythi—and he was from his kin—narrated to us, saying: The Messenger of Allah (may Allah bless him and grant him peace) sent out a military detachment, and it raided a people. A man from the people fled, and a man from the detachment followed him, with his sword drawn. The man from the people said, "I am a Muslim, I am a Muslim." But he did not consider that, and he struck him and killed him. The news reached the Messenger of Allah (may Allah bless him and grant him peace), and he spoke harshly regarding it. This reached the killer. He said: While the Messenger of Allah (may Allah bless him and grant him peace) was delivering a sermon, the killer said, "O Messenger of Allah, by Allah, he did not say what he said except to seek refuge from being killed." The Messenger of Allah (may Allah bless him and grant him peace) turned away from him and from the people who were before him, and continued his sermon. He said: Then he returned and said, "O Messenger of Allah, he did not say what he said except to seek refuge from being killed." The Messenger of Allah (may Allah bless him and grant him peace) turned away from him and from the people who were before him. He could not be patient, so he said it a third time. He (the Prophet) turned toward him, and displeasure was recognizable on his face, and he said, "Verily, Allah the Almighty and Majestic has refused for me to kill a believer," three times.