The report of Salim is authentic, but it does not establish a general permission for women to breastfeed adult men. The mainstream ruling is that milk kinship is established during infancy; the case of Salim was treated either as a special dispensation or, by most jurists, as a ruling confined to that particular circumstance.
Why critics find the report troubling
The objection is serious: Sahla bint Suhayl was instructed to breastfeed Salim, a grown man living in her household, so that he would become her foster son and could enter freely. Taken as a universal rule, this seems strange, open to abuse, and inconsistent with the normal boundaries of modesty. It is therefore reasonable to ask whether the report was invented to solve a private domestic inconvenience.
What the report actually says
The setting matters. Salim had been raised in the household of Abu Hudhayfa and Sahla through the pre-Islamic practice of adoption. After Islam abolished the legal fiction that an adopted child becomes identical to a biological child, Salim's status created a real difficulty for a household in which he had already grown up. The Prophet (PBUH) addressed that exceptional case directly:
Sahla bint Suhayl came to the Prophet and said, "O Messenger of Allah, we regard Salim as our son, and he enters upon me while Abu Hudhayfa feels discomfort." The Prophet (PBUH) said, "Breastfeed him, and he will become unlawful for you to marry."
Sahih Muslim 1453
This was not presented as a casual method for creating intimacy between unrelated adults. The purpose was to establish a legal foster relationship in an unusual household arrangement. Milk kinship itself creates restrictions: the person becomes permanently unmarriageable, just as a biological relative is. It does not grant sexual access or erase rules of modesty.
Why it is not the general law
The Quran places nursing within early childhood:
Mothers shall nurse their children for two whole years, for those who wish to complete the nursing.
Quran 2:233
It also describes milk mothers and milk sisters among those whom one may not marry (Quran 4:23). On this basis, the four major Sunni schools generally hold that nursing after infancy does not create milk kinship. They understood the Salim report as a special case, or as an exceptional ruling that was not extended to the community. Aisha held the broader interpretation, but the other wives of the Prophet (PBUH) rejected applying it generally, and the majority followed their position.
Thus the report does not support a routine practice of adult women nursing unrelated men. It records an exceptional legal solution to an exceptional household problem. One may debate the wisdom of that solution, but calling it a self-serving fabrication ignores both its authentic transmission and the fact that the dominant legal tradition deliberately refused to generalize it.