Jami` at-Tirmidhi 1196
Humaid bin Nafi narrated that :
Zainab said: "So I entered upon Zainab bint Jahsh when her brother died. She called for some perfume and put it on, then said: 'By Allah! I have no need for perfume except that I heard the Messenger of Allah said: "It is not lawful for a woman who believes in Allah and the Last Day to mourn for the dead more than three nights, except for her husband (in which case it is) four months and ten days."
قَالَتْ زَيْنَبُ فَدَخَلْتُ عَلَى زَيْنَبَ بِنْتِ جَحْشٍ حِينَ تُوُفِّيَ أَخُوهَا فَدَعَتْ بِطِيبٍ فَمَسَّتْ مِنْهُ ثُمَّ قَالَتْ وَاللَّهِ مَا لِي فِي الطِّيبِ مِنْ حَاجَةٍ غَيْرَ أَنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏
"‏ لاَ يَحِلُّ لاِمْرَأَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثِ لَيَالٍ إِلاَّ عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏"‏ ‏.‏