Musnad Ahmad 1169:1

Yunus ibn Muhammad narrated to us, he said: Hammad—meaning Ibn Salamah—narrated to us, from Abd al-Rahman ibn al-Qasim, from al-Qasim ibn Muhammad, from Sahlah, the wife of Abu Hudhayfah, that she said: I said: "O Messenger of Allah, Salim, the freed slave of Abu Hudhayfah, enters upon me, and he has a beard." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Breastfeed him." She said: "How shall I breastfeed him when he has a beard?" So she breastfed him, and he used to enter upon her.