The Prophet (ﷺ) said, "It is not lawful for a Muslim woman who believes in Allah and the Last Day to mourn for more than three days, except for her husband, for whom she should mourn for four months and ten days."
Sahih al-Bukhari Book 68, Hadith 84
← Previous Hadith A woman was bereaved of her husband and her relatives worried about her eyes (which were diseased). They came to Allah's Messenger (ﷺ), and asked him to allow them to treat her eyes with kohl, but he said, "She should not apply kohl to her eyes. (In the Pre-Islamic period of Ignorance) a widowed woman among you would stay in the worst of her clothes (or the worst part of her house) and when a year had elapsed, if a dog passed by her, she would throw a globe of dung, Nay, (she cannot use kohl) till four months and ten days have elapsed."

Sahih al-Bukhari Book 68, Hadith 83 Next Hadith → We were forbidden to mourn for more than three days except for a husband.

Sahih al-Bukhari Book 68, Hadith 85