Sahih Bukhari Volume 7, Book 76, Hadith 5708

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ شُعْبَةَ، قَالَ حَدَّثَنِي حُمَيْدُ بْنُ نَافِعٍ، عَنْ زَيْنَبَ، عَنْ أُمِّ سَلَمَةَ ـ رضى الله عنها ـ أَنَّ امْرَأَةً تُوُفِّيَ زَوْجُهَا فَاشْتَكَتْ عَيْنَهَا، فَذَكَرُوهَا لِلنَّبِيِّ صلى الله عليه وسلم وَذَكَرُوا لَهُ الْكُحْلَ، وَأَنَّهُ يُخَافُ عَلَى عَيْنِهَا، فَقَالَ ‏"‏ لَقَدْ كَانَتْ إِحْدَاكُنَّ تَمْكُثُ فِي بَيْتِهَا فِي شَرِّ أَحْلاَسِهَا ـ أَوْ فِي أَحْلاَسِهَا فِي شَرِّ بَيْتِهَا ـ فَإِذَا مَرَّ كَلْبٌ رَمَتْ بَعْرَةً، فَلاَ، أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏"

Narrated By Um Salama : The husband of a lady died and her eyes became sore and the people mentioned her story to the Prophet They asked him whether it was permissible for her to use kohl as her eyes were exposed to danger. He said, "Previously, when one of you was bereaved by a husband she would stay in her dirty clothes in a bad unhealthy house (for one year), and when a dog passed by, she would throw a globe of dung. No, (she should observe the prescribed period Idda) for four months and ten days."