Yahya related to me from Malik from Nafi from Safiyya bint Abi Ubayd from A'isha and Hafsa, the wives of the Prophet ﷺ that the Messenger of Allah ﷺ 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."
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ