"Then I went into Zainab bint Jahsh when her brother died, and she called for some perfume and put some on. Then she said: 'By Allah, I do not have any need for perfume but I heard the Messenger of Allah say on the Minbar: It is not permissible for any woman who believes in Allah and the Last Day to mourn for anyone who dies for more than three days, except for a husband, (for whom the mourning period is) four months and ten days.'" (Using translation from Nasāʾī 3533b)
أَنَّهَا دَخَلَتْ عَلَى زَيْنَبَ بِنْتِ جَحْشٍ زَوْجِ النَّبِيِّ ﷺ فَقَالَتْ إِنِّي سَمِعْتُ رَسُولَ اللهِ ﷺ عَلَى الْمِنْبَرِ يَقُولُ لَا يَحِلُّ لِامْرَأَةٍتُؤْمِنُ بِاللهِ وَالْيَوْمِ الْآخِرِ أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلَاثِ لَيَالٍ إِلَّا عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا