It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Sayyidah Sahlah bint Suhayl bin Amr (may Allah be pleased with her) came to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah, Salim, the freed slave of Abu Hudhayfah (may Allah be pleased with him), lives with us in our house, and he has reached the age that men reach and knows what men know. The Prophet (peace and blessings be upon him) said: "Nurse him, and you will become unlawful (for marriage) to him."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21107