The Messenger of Allah ﷺ said, "It is not permissible for a woman who believes in Allah to mourn for more than three days, except for her husband."
حدثنا هاشم بن القاسم قال حدثنا ورقاء عن عبد الله بن دينار قال سمعت صفية تقول قالت
قال رسول الله ﷺ لا يحل لامرأة تؤمن بالله أن تحد فوق ثلاثة أيام إلا على زوجها
Its isnad is sahih, it previously appeared at 23974. Warqa is Ibn Umar al-Yashkuri, and he is trustworthy, his hadith is found in the collections of the entire group (al-Jamaah).