سنن النسائي

It was narrated from Zainab bint Umm Salamah -I (the narrator) said: "From her mother?" He said: "Yes" - "that the Prophet (ﷺ) 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)."