Musnad Ahmad 25:875

Hujayn ibn al-Muthanna narrated to me, Isra’il narrated to us, from ‘Abd al-A‘la, from Ibn Jubayr, from Ibn ‘Abbas: That a man from the Ansar insulted the father of al-‘Abbas, who was in the Jahiliyyah (pre-Islamic era), so al-‘Abbas slapped him. His people came and said: "By Allah, we will surely slap him just as he slapped him." They put on their weapons, and that reached the Messenger of Allah, peace and blessings of Allah be upon him. He ascended the pulpit and said: "O people, which of the people of the earth is most noble to Allah?" They said: "You." He said: "Indeed, al-‘Abbas is from me, and I am from him. So do not insult our dead, for you will harm our living." The people came and said: "O Messenger of Allah, we seek refuge in Allah from your anger."