Sunan an-Nasa'i, Volume 4, Book 27, Hadith 3531 (DarusSalam) ⓘ

It was narrated from Zainab bint Umm Salamah -I (the narrator) said: "From her mother?" He said: "Yes" - "that the Prophet was asked about a woman whose husband had died but they were worried about her eyes - could she use kohl?" He said: "One of you used to stay in her house wearing her shabbiest clothes for a year, then she would come out. No, (the mourning period is) four months and ten (days)."

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ حُمَيْدِ بْنِ نَافِعٍ، عَنْ زَيْنَبَ بِنْتِ أُمِّ سَلَمَةَ، قُلْتُ عَنْ أُمِّهَا، قَالَ نَعَمْ إِنَّ النَّبِيَّ صلى الله عليه وسلم سُئِلَ عَنِ امْرَأَةٍ تُوُفِّيَ عَنْهَا زَوْجُهَا فَخَافُوا عَلَى عَيْنِهَا أَتَكْتَحِلُ فَقَالَ ‏ "‏ قَدْ كَانَتْ إِحْدَاكُنَّ تَمْكُثُ فِي بَيْتِهَا فِي شَرِّ أَحْلاَسِهَا حَوْلاً ثُمَّ خَرَجَتْ فَلاَ أَرْبَعَةَ أَشْهُرٍ وَعَشْرًا ‏" ‏ ‏.‏