Musnad Ahmad 1156:180

Muhammad ibn Ja‘far narrated to us, Shu‘bah and Hajjaj narrated to us, he said: Shu‘bah narrated to me, from Humayd ibn Nafi‘, he said: I heard Zaynab bint Abi Salamah narrating from her mother, that a woman’s husband died, and they feared for her eye, so they came to the Prophet, peace and blessings of Allah be upon him, and asked his permission regarding kohl. The Messenger of Allah, peace and blessings of Allah be upon him, said: "One of you would be in her house in her rags, or in the worst of her rags in her house, for a year. Then, if a dog passed by, she would throw a piece of dung at it, and then she would go out. So, it is not [more than] four months and ten [days]."