Breastfeeding a husband in Islam is a complex topic with differing opinions. According to some scholars, it is not forbidden but strongly discouraged, as it is considered a great sin [https://islamqa.org/hanafi/askimam/1029/i-want-to-know-the-point-of-view-of-islam-regarding-to-breastfeeding-to-husband-is-that-allowed-in-islam-if-no-then-how-should-i-behave-with-my-husband-if-he-pressurizes-me/].
The main reason for this view is that breastfeeding has a significant legal implication in Islam, creating a relationship of mahram (prohibition of marriage) between the breastfeeding person and the recipient. The breastfeeding must be for nourishment, not merely symbolic or for pleasure [https://islamqa.info/en/answers/2864/can-husband-drink-milk-of-wife-in-islam].
Therefore, a wife breastfeeding her husband does not create a mahram relationship since the purpose is not for nourishment but for sexual pleasure [https://www.quora.com/Can-a-wife-breastfeed-her-husband-during-menstruation-in-Islam]. While it might be permissible, many scholars discourage it due to its perceived resemblance to sexual activity.
In conclusion, while there is no definitive prohibition, the general consensus is that breastfeeding a husband in Islam is highly discouraged due to its potential for misinterpretation and deviation from the purpose of breastfeeding.
