Is saying, "The Prophet's daughter was an adulteress," considered disbelief (kufr)? Does this mean that the honor of the messengers and prophets is safeguarded from adultery, or is it not safeguarded, but it is impermissible to say such things due to the disrespect it implies towards the Prophet, even though a prophet's sister, daughter, or mother could potentially commit adultery?

Accusing a Prophet's wife of adultery with the aim of insulting or reviling the Prophet is an act of disbelief (kufr). Accusing the Prophet's mother of adultery is disbelief and necessitates execution. The Prophet's mother, Mary, was infallible against adultery, and to disbelieve the Qur’an is disbelief. Insulting Fatimah, the Prophet's daughter, is considered disbelief. The wives of Prophets are infallible against immorality, and the betrayal of Noah's and Lot's wives was in religion, not in adultery.