Yahya related to me from Malik from Nafi from Safiyya bint Abi
Ubayd from A'isha and Hafsa, the wives of the Prophet, may Allah bless
him and grant him peace, that the Messenger of Allah, may Allah bless
him and grant him peace, said, "It is not halal for a woman in
mourning for someone who has died, if she trusts in Allah and the Last
Day, to abstain from adornment for more than three nights, except for
a husband."
Muwatta Malik Book 29, Hadith 115