Riyad as-Salihin, Book 18, Hadith 1750 (In-Book)

Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah 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].

عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏ "‏لا يحل للمرأة أن تصوم وزوجها شاهد إلا بإذنه، ولا تأذن في بيته إلا بإذنه‏" ‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏

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