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)”"
SahihSahihSahih - Agreed UponBook 27 · Hadith 112