Sahih Muslim Book 9, Hadith Number 3541.
Chapter: It is obligatory to abstain from adornment during the ‘Idda period, but mourning beyond three days is prohibited.
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 (may peace be upon him) and sought permission for the use of collyrium, whereupon Allah’s Messenger (may peace be upon him) 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?