Language:
كتاب الطلاق
68
Divorce
(47)
Chapter: Can a mourning lady use kohl?
(47)
باب الْكُحْلِ لِلْحَادَّةِ
Sahih al-Bukhari 5339

Narrated Um Habiba:

The Prophet (ﷺ) said, "It is not lawful for a Muslim woman who believes in Allah and the Last Day to mourn for more than three days, except for her husband, for whom she should mourn for four months and ten days."

وَسَمِعْتُ زَيْنَبَ ابْنَةَ أُمِّ سَلَمَةَ، تُحَدِّثُ عَنْ أُمِّ حَبِيبَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏ "‏ لاَ يَحِلُّ لاِمْرَأَةٍ مُسْلِمَةٍ تُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الآخِرِ أَنْ تُحِدَّ فَوْقَ ثَلاَثَةِ أَيَّامٍ، إِلاَّ عَلَى زَوْجِهَا أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏"‏‏.‏
Reference : Sahih al-Bukhari 5339
In-book reference : Book 68, Hadith 84
USC-MSA web (English) reference : Vol. 7, Book 63, Hadith 252
  (deprecated numbering scheme)