Sahih Bukhari Volume 7, Book 68, Hadith 5337

قَالَتْ زَيْنَبُ فَدَخَلْتُ عَلَى زَيْنَبَ ابْنَةِ جَحْشٍ حِينَ تُوُفِّيَ أَخُوهَا، فَدَعَتْ بِطِيبٍ فَمَسَّتْ مِنْهُ، ثُمَّ قَالَتْ أَمَا 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 أَنْ تُحِدَّ عَلَى مَيِّتٍ فَوْقَ ثَلاَثِ لَيَالٍ إِلاَّ عَلَى زَوْجٍ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏"‏‏

Zainab further said, "I heard my mother, Um Salama saying that a woman came to Allah's Apostle and said, "O Allah's Apostle! The husband of my daughter has died and she is suffering from an eye disease, can she apply kohl to her eye?" Allah's Apostle replied, "No," twice or thrice. (Every time she repeated her question) he said, "No." Then Allah's Apostle added, "It is just a matter of four months and ten days. In the Pre-Islamic Period of ignorance a widow among you should throw a globe of dung when one year has elapsed."