Riyad as-Salihin 17:240

Abu Hurairah (May Allah be pleased with him) said:

The Messenger of Allah (ﷺ) said, "It is not lawful for a woman to observe an optional Saum (fast) without the permission of her husband when he is at home. Nor should she allow anyone to enter his house without his permission." [Al-Bukhari and Muslim] .