It is narrated from Ya'la bin Umayyah that Umar bin Khattab (may Allah be pleased with him) was performing ghusl behind a camel and I was holding a cloth as a screen for him, when Umar bin Khattab (may Allah be pleased with him) said: "O Ya'la! Pour water over my head." So I said: "Ameer al-Mu'mineen knows best." Then Umar bin Khattab (may Allah be pleased with him) said: "By Allah! Water only increases the hair in disarray." Then he mentioned the name of Allah and poured water over his head.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 861
Hadith Takhrijاسناده ضعيف لإنقطاعة بين عطله اخرجه البيهقي : 5 / 63 ـ وفي المعرفة السنن والآثار له (2867)۔