Musnad Ahmad 1273:5

Yahya narrated to us, from Shu'bah, who said: Humayd ibn Nafi' narrated to me, from Zaynab bint Abi Salamah, that a relative of Umm Habibah died, so she called for some yellow perfume and wiped her forearms with it. She said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) — or he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "It is not permissible for a woman who believes in Allah and the Last Day to mourn for a dead person for more than three days, except for a husband, for she shall mourn for him for four months and ten days."