Musnad Ahmad 174:1

Yazid narrated to us, he said: Al-Mustalim ibn Sa'id informed us, Khabib ibn 'Abd al-Rahman narrated to us, from his father, from his grandfather, who said: I came to the Messenger of Allah, peace and blessings of Allah be upon him, while he was intending to go on a military expedition, along with a man from my people, and we had not yet embraced Islam. We said: "We are ashamed that our people should witness a scene that we do not witness with them." He said: "Have you both embraced Islam?" We said: "No." He said: "Then we do not seek the help of the polytheists against the polytheists." He said: So we embraced Islam and witnessed it with him. I killed a man, and he struck me a blow, and I married his daughter after that. She used to say: "May I never lose a man who adorned you with this adornment [the scar]." And I would say: "May I never lose a man who hastened your father to the Fire."