question #3 Sahih Muslim 939f, Book 11, Hadith 51 : Why might the Prophet Muhammad (ﷺ) have instructed the use of his under-garment for Zainab’s burial preparation?

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.”