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." (TR)
English reference (TR): Vol. 3, Book 10, Hadith 2086 (TR)
Arabic reference (TR): Book 10, Hadith 2164 (TR)