This hadith was narrated by Zainab from her mother and from Zainab, the wife of Allah's Apostle (ﷺ), or from some other lady from among the wives of the Prophet (ﷺ)

Zainab bint Umm Salama (Allah be pleased with her) reported on the authority of her mother that a woman lost her husband. (As her eyes were ailing) they (her kith and kin) entertained fear about her eyes, so they came to Allah's Apostle (ﷺ) and sought permission for the use of collyrium, whereupon Allah's Messenger (ﷺ) said:One among you used to spend one year in a dungeon dressed in worst clothes. (And at the end of this period) she threw dung at the dog which happened to pass that way and then she came out (of her 'Idda). Can't she (wait) even for four months and ten days?

Humaid b. Nafi' narrated two traditions from Umm Salama dealing with collyrium and the other hadith from the wives of Allah's Prophet (ﷺ) except with this that no mention was made of Zainab