Musnad Ahmad 626:21

Abu Mu'awiyah narrated to us, 'Asim narrated to us, from Bakr ibn 'Abdullah, from al-Mughirah ibn Shu'bah, who said: I proposed to a woman, and the Messenger of Allah (peace and blessings of Allah be upon him) said to me: "Have you looked at her?" I said: "No." He said: "Then look at her, for it is more likely that there will be harmony between you."