Jami` at-Tirmidhi 1196

Humaid bin Nafi narrated that :Zainab said: "So I entered upon Zainab bint Jahsh when her brother died. She called for some perfume and put it on, then said: 'By Allah! I have no need for perfume except that I heard the Messenger of Allah said: "It is not lawful for a woman who believes in Allah and the Last Day to mourn for the dead more than three nights, except for her husband (in which case it is) four months and ten days