It was narrated from 'Aishah that:
the Prophet (ﷺ) said: "It is not permissible for a woman to mourn for any deceased person for more than three days, except for her husband." (IT)
English reference (IT): Vol. 3, Book 10, Hadith 2085 (IT)
Arabic reference (IT): Book 10, Hadith 2163 (IT)