Zaynab bint Umm Salama reported,

I went in to see Zaynab bint Jahsh when her brother died. She called for perfume and applied some of it, then said, "By Allah, I have no need for perfume, but I heard the Messenger of Allah ﷺ say from the pulpit, 'It is not lawful for a woman who believes in Allah and the Last Day to mourn for any deceased person more than three nights, except for a husband, for whom she mourns four months and ten days.'"

Bukhari 5335

Sahih

قالت زينب

فدخلت على زينب بنت جحش حين توفي أخوها فدعت بطيب فمست منه ثم قالت أما والله ما لي بالطيب من حاجة غير أني سمعت رسول الله ﷺ يقول على المنبر لا يحل لامرأة تؤمن بالله واليوم الآخر أن تحد على ميت فوق ثلاث ليال إلا على زوج أربعة أشهر وعشرا

البخاري 5335صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Divorce
Chapter
A widow's mourning period of four months and ten days
Numbering
Darussalam 5335
Bukhari 5335