Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 2046
Umm 'Atiyya reported: When Zainab the daughter of the Messenger of Allah (may peace be upon him) died, he said to us: Wash her odd number of times, i. e. three or five times, and put camphor or something-like camphor at the fifth time, and after you have washed her inform me. So we informed him and he gave us his under-garment, saying:" Put it next her body."