Sahih Muslim 1488 c
Zainab bint Umm Salama (Allah be pleased with her) reported on the authority of her mother that a woman lost her husband. (As her eyes were ailing) they (her kith and kin) entertained fear about her eyes, so they came to Allah's Apostle (ﷺ) and sought permission for the use of collyrium, whereupon Allah's Messenger (ﷺ) said:
One among you used to spend one year in a dungeon dressed in worst clothes. (And at the end of this period) she threw dung at the dog which happened to pass that way and then she came out (of her 'Idda). Can't she (wait) even for four months and ten days?
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ حُمَيْدِ بْنِ نَافِعٍ، قَالَ سَمِعْتُ زَيْنَبَ بِنْتَ أُمِّ سَلَمَةَ، تُحَدِّثُ عَنْ أُمِّهَا، أَنَّ امْرَأَةً، تُوُفِّيَ زَوْجُهَا فَخَافُوا عَلَى عَيْنِهَا فَأَتَوُا النَّبِيَّ صلى الله عليه وسلم فَاسْتَأْذَنُوهُ فِي الْكُحْلِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ قَدْ كَانَتْ إِحْدَاكُنَّ تَكُونُ فِي شَرِّ بَيْتِهَا فِي أَحْلاَسِهَا - أَوْ فِي شَرِّ أَحْلاَسِهَا فِي بَيْتِهَا - حَوْلاً فَإِذَا مَرَّ كَلْبٌ رَمَتْ بِبَعَرَةٍ فَخَرَجَتْ أَفَلاَ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏"‏ ‏.‏