Hadith 27:146
Zainab said:
"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.'"
قَالَتْ زَيْنَبُ ثُمَّ دَخَلْتُ عَلَى زَيْنَبَ بِنْتِ جَحْشٍ حِينَ تُوُفِّيَ أَخُوهَا وَقَدْ دَعَتْ بِطِيبٍ وَمَسَّتْ مِنْهُ ثُمَّ قَالَتْ وَاللَّهِ مَا لِي بِالطِّيبِ مِنْ حَاجَةٍ غَيْرَ أَنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ عَلَى الْمِنْبَرِ " لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ تَحِدُّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثِ لَيَالٍ إِلاَّ عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا "
Original Reference: Sunan an-Nasa'i 3533b