Sayyidah Aishah (may Allah be pleased with her) narrates 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 - meaning Salim, the freed slave of Hudhayfah - lives with us in our house, and he has reached what men reach, and he knows what men know. The Prophet (peace and blessings be upon him) said: "Suckle him, and you will become unlawful (for marriage) to him."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6343