It was narrated from Hafsah the wife of the Prophet (ﷺ) that:
the Messenger of Allah (ﷺ), said: "It is not permissible for a woman who believes in Allah and the Last Day to mourn for any deceased person for more than three days, except for her husband." (ID)
English reference (ID): Vol. 3, Book 10, Hadith 2086 (ID)
Arabic reference (ID): Book 10, Hadith 2164 (ID)