(55) باب عِدَّةِ الْمُتَوَفَّى عَنْهَا زَوْجُهَا
It was narrated from Safiyyah bint Abi 'Ubaid that she heard Hafsah bint 'Umar, the wife of the Prophet, (narrate) that the Prophet said:
"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 should mourn for him for four months and ten (days)."
Reference: Sunan an-Nasa'i 3503
In-book reference: Book 27, Hadith 115
English translation: Vol. 4, Book 27, Hadith 3533