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." (DE)
English reference (DE): Vol. 3, Book 10, Hadith 2085 (DE)
Arabic reference (DE): Book 10, Hadith 2163 (DE)