Musannaf Ibn Abi Shayba 36:415

Hussayn ibn Ali narrated to us, from Hamzah al-Zayyat, who said: When the day of the conquest of Makkah arrived, the Messenger of Allah (may Allah bless him and grant him peace) entered from the upper part of Makkah, and Khalid ibn al-Walid entered from the lower part of Makkah. He said: The Messenger of Allah (may Allah bless him and grant him peace) said, "Do not kill," and he placed his hand against the killing. The Messenger of Allah (may Allah bless him and grant him peace) said, "Do not kill," and he placed his hand against the killing. Then he said, "What compelled you to do what you did?" He replied, "O Messenger of Allah, I was not able to do anything other than what I did."