Sahih Muslim Book 9, Hadith Number 3543.

Chapter: It is obligatory to abstain from adornment during the ‘Idda period, but mourning beyond three days is prohibited.

Zainab bint Abu Salama reported: Umm Salama and Umm Habiba (Allah be pleased with them) were talking with each other (and saying) that a woman came to Allah’s Messenger (may peace be upon him) and mentioned to him that her daughter had lost her husband, and her eyes were sore and she wanted to use collyrium, whereupon Allah’s Messenger (may peace be upon him) said: One among you used to throw dung at the end of a year, and now (this abstinence from adornment) is only for four months and ten days.