Musnad Ahmad 1153:2311

Ya'qub narrated to us, he said: Ibn Akhi Ibn Shihab narrated to us, from his uncle, who said: 'Urwah ibn al-Zubayr informed me, from 'Aishah, she said: Sahlah bint Suhayl ibn 'Amr, who was the wife of Abu Hudhayfah ibn 'Utbah, came to the Messenger of Allah (peace and blessings of Allah be upon him) and said: "Salim, the freed slave of Abu Hudhayfah, enters upon us, and we have surplus [space/time], and we used to consider him a son. Abu Hudhayfah had adopted him just as the Messenger of Allah (peace and blessings of Allah be upon him) adopted Zayd." Then Allah revealed: "Call them by [the names of] their fathers; it is more just in the sight of Allah" [Al-Ahzab: 5]. So the Messenger of Allah (peace and blessings of Allah be upon him) commanded her at that time to breastfeed Salim. She breastfed him five times, and he became in the position of her son through breastfeeding. Because of that, 'Aishah used to command her sisters and the daughters of her brothers to breastfeed whoever 'Aishah loved to see her and enter upon her, even if he were an adult, five times; then he would enter upon them. Umm Salamah and the rest of the wives of the Prophet (peace and blessings of Allah be upon him) refused to let anyone enter upon them through that breastfeeding unless he was breastfed in the cradle. They said to 'Aishah: "By Allah, we do not know; perhaps it was a concession from the Messenger of Allah (peace and blessings of Allah be upon him) for Salim specifically, excluding the rest of the people."