Musannaf Ibn Abi Shayba 36:370

Yazid ibn Harun narrated to us, he said: Husayn al-Mu'allim narrated to us, from 'Amr ibn Shu'ayb, from his father, from his grandfather, that the Prophet, may Allah bless him and grant him peace, said on the day of the conquest of Mecca: "Restrain your weapons, except for Khuza'a against Banu Bakr." So he gave them permission until they prayed the Asr prayer, then he said to them: "Restrain your weapons." The next day, a man from Khuza'a met a man from Banu Bakr and killed him at al-Muzdalifah. This reached the Messenger of Allah, may Allah bless him and grant him peace, so he stood up to deliver a sermon and said: "Indeed, the most hostile of people toward Allah is he who kills in the Sacred Precinct, and he who kills someone other than his killer, and he who kills for the blood feuds of the Pre-Islamic Era (Jahiliyyah)."