Ja'far bin Muhammad relates from his father that Sayyidah Umm Salamah (may Allah be pleased with her) said: O Messenger of Allah! A woman whose husband has died: do you permit her to apply kohl? He (peace and blessings be upon him) said: "When the husband of one of you died, she would take a piece of camel dung and throw it behind her back, then say: I will not apply kohl until this piece of dung changes. Yet the waiting period is only four months and ten days."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20285