Sahih al-Bukhari 5338
Narrated Um Salama:
A woman was bereaved of her husband and her relatives worried about 
     her eyes (which were diseased). They came to Allah's Messenger (ﷺ), and 
     asked him to allow them to treat her eyes with kohl, but he said, "She
     should not apply kohl to her eyes. (In the Pre-Islamic period of 
     Ignorance) a widowed woman among you would stay in the worst of her 
     clothes (or the worst part of her house) and when a year had elapsed, 
     if a dog passed by her, she would throw a globe of dung, Nay, (she 
     cannot use kohl) till four months and ten days have elapsed."
حَدَّثَنَا آدَمُ بْنُ أَبِي إِيَاسٍ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا حُمَيْدُ بْنُ نَافِعٍ، عَنْ زَيْنَبَ ابْنَةِ أُمِّ سَلَمَةَ، عَنْ أُمِّهَا، أَنَّ امْرَأَةً، تُوُفِّيَ زَوْجُهَا فَخَشُوا عَلَى عَيْنَيْهَا فَأَتَوْا رَسُولَ اللَّهِ صلى الله عليه وسلم فَاسْتَأْذَنُوهُ فِي الْكُحْلِ فَقَالَ ‏
"‏ لاَ تَكَحَّلْ قَدْ كَانَتْ إِحْدَاكُنَّ تَمْكُثُ فِي شَرِّ أَحْلاَسِهَا أَوْ شَرِّ بَيْتِهَا، فَإِذَا كَانَ حَوْلٌ فَمَرَّ كَلْبٌ رَمَتْ بِبَعَرَةٍ، فَلاَ حَتَّى تَمْضِيَ أَرْبَعَةُ أَشْهُرٍ وَعَشْرٌ ‏"‏‏.‏