Al-Matalib al-'Aliyah 162 — Covering oneself when performing ghusl

It is narrated from Sayyiduna Ya'la bin Umayyah (may Allah be pleased with him) that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) was taking a bath behind the cover of his camel while in the state of ihram, and I was screening him with a cloth. Meanwhile he said to me: "O Ya'la! Pour water on my head." I said: The Commander of the Believers knows better (whether doing so in ihram is proper or not). He said: "By Allah! I consider that water does nothing to the hair except make it more dishevelled and unkempt (that is, it does not cause hair to break)." Then he said 'Bismillah' (In the name of Allah) and poured water over his head.
The chain of this narration is sahih (authentic), and its basis is found in Sahih al-Bukhari (1840) and Sahih Muslim (1206).