Safiyyah bint Abi Ubayd narrates that she heard Hafsah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), relate that the Prophet (peace and blessings be upon him) said: "It is not permissible for a woman who believes in Allah and the Last Day to mourn for a deceased person for more than three days, except for a husband."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19692