Sahih al-Bukhari 5338

Narrated Um Salama:

A woman was bereaved of her husband and her relatives worried about
her eyes (which were diseased). They came to Allah’s Messenger, and
asked him to allow them to treat her eyes with kohl, but he said, “She
should not apply kohl to her eyes. (In the Pre-Islamic period of
Ignorance) a widowed woman among you would stay in the worst of her
clothes (or the worst part of her house) and when a year had elapsed,
if a dog passed by her, she would throw a globe of dung, Nay, (she
cannot use kohl) till four months and ten days have elapsed.”