Hadith #1820 (Sunan Ibn Majah)
Book: The Chapters on Divorce
Narrator(s): Abu Bakr bin Abi Shayba أبو بكر بن أبي شيبة, Ali bin Muhammad bin Ishaq al-Tanafasi علي بن محمد بن إسحاق الطنافسي, Habib bin Zayd bin Khallad حبيب بن زيد بن خلاد, Sahl bin Sa'd bin Malik, Shu'bah bin al-Hajjaj شعبة بن الحجاج, Umm 'Ammarah Nasaybah, Waki' bin al-Jarrah وكيع بن الجراح

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.”

Source: https://parallelquran.com/hadith/sunan-ibn-majah-1820/