Sunan an Nasai
3527
Sahih+2

It was narrated from Zainab bint Abi Salamah that Umm Habibah said:"I heard the Messenger of Allah say this on this Minbar: 'It is not permissible for a woman who believes in Allah and His Messenger to mourn for anyone who dies for more than three days, except for a husband, (for whom the mourning period is) four months and ten days

SahihAbu Ghuddah
SahihAl-Albani