´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."
Hadith Referenceسنن ابن ماجه / كتاب الطلاق / 2086
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم
´It was narrated from Safiyyah bint Abi 'Ubaid that she heard Hafsah bint 'Umar, the wife of the Prophet, (narrate) that the Prophet said:` "It is not permissible for a woman who believes in Allah and the Last Day to mourn for anyone who dies for more than three days except for a husband; she should mourn for him for four months and ten (days)."
Hafiz Muhammad Ameen
Urdu marginal note: By mourning (sawg) is meant to abstain from something permissible, not to commit something forbidden, such as screaming, wailing, striking the cheeks, lamenting, shaving the head, etc. Mourning for more than three days is also prohibited for men. Women are mentioned specifically because they tend to mourn more. Men generally possess more forbearance.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3533