Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.023.

It is permissible for a woman to mourn for a period of three days on the death of a near relative, provided that her husband does not object to her doing so. It is not permissible for her to mourn for more than three days, except in the case of her husband’s death, when she is to mourn for four months and ten days, which is a legally prescribed period of waiting or “iddah”. This is reported by the group, (The compilers of the six most reliable hadith books generally known as Sihah Sitta) except Tirmizhi. They report from Umm ‘Atiyyah, that the Messenger of Allah said: “A woman should not mourn for any deceased person for more than three days, except in the case of her husband’s death, which she may mourn for a period of four months and ten days. Such a woman (in mourning) is not to wear any (brightly) coloured dress. She may wear only plain dress. During this period she should not use any adornment or eye makeup, nor wear any perfume, nor dye her hands and feet with henna, nor comb her hair, except at the end of her menstruation period, when she may use some cleaning or refreshing agents (such as perfume, etc.) to get rid of any offensive smell left over from her period.” Accordingly, when a widow mourns, she must not use any adornment, such as jewellery, kohl, 58 silk, perfume, or henna dye on her hands and feet. A widow must observe this waiting period in deference to her late husband’s memory and to fulfil her obligations toward him.