Sahih Muslim 1453b

Sahlah bint Suhayl, the wife of Abu Hudhayfah, sought a legal opinion concerning Sālim, one of the meritorious Companions. Her husband Abu Hudhayfah had adopted Sālim when adoption was still permissible and was not yet abrogated. Sālim grew up under the care of Abu Hudhayfah and his wife like a son to both of them. However, when Allah, the Almighty, revealed: {Call them by [the names of] their fathers}, adoption became forbidden.

As long as he was still young, Sālim was entering and exiting the house in which Sahlah lived. He accessed the house freely until he grew up into an adult man, and he would still see Sahlah. Abu Hudhayfah did not like that, but it was difficult for the spouses to deny Sālim access given their amicable relationship with him.

Hence, they asked the Messenger of Allah (may Allah's peace and blessings be upon him) about that, to which he said to Sahlah: "Suckle him so that you will be forbidden to him." Thus Abu Hudhayfah's aversion would wear out. Sahlah suckled him, and the matter was settled. It should be noted, however, that this ruling is specific to that case, for anyone who was suckled by a woman after he had been weaned, the sucking woman would not become his foster mother, as the Permanent Committee stated.