From Sahih Muslim (Hadith 3603):
Umm Salama said to 'A'isha (Allah be pleased with her):A young boy who is at the threshold of puberty comes to you. I, however, do not like that he should come to me, whereupon 'A'isha (Allah be pleased with her) said: Don't you see in Allah's Messenger (ﷺ) a model for you? She also said: The wife of Abu Hudhaifa said: Messenger of Allah, Salim comes to me and now he is a (grown-up) person, and there is something that (rankles) in the mind of Abu Hudhaifa about him, whereupon Allah's Messenger (ﷺ) said: Suckle him (so that he may become your foster-child), and thus he may be able to come to you (freely)
Reference: Muslim 3603