From Sahih Muslim (Hadith 2173):
Umm 'Atiyya reported:When Zainab the daughter of the Messenger of Allah (ﷺ) 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
Reference: Muslim 2173