(55) باب عِدَّةِ الْمُتَوَفَّى عَنْهَا زَوْجُهَا
It was narrated that Zainab bint Umm Salamah said:
"Umm Habibah said: 'I heard the Messenger of Allah say: It is not permissible for a woman who believes in Allah and the Last Day to mourn for anyone who dies for more than three days, except for a husband; (she mourns for him for) four months and ten (days)."
Reference: Sunan an-Nasa'i 3500
In-book reference: Book 27, Hadith 112
English translation: Vol. 4, Book 27, Hadith 3530