From Sahih Muslim (Hadith 743):
Jabir b. 'Abdullah reported:When the Messenger of Allah (ﷺ) took a bath because of sexual intercourse, he poured three handfuls of water upon his head. Hasan b. Muhammad said to him (the narrator): My hair is thick. Upon this Jabir observed. I said to him: O son of my brother, the hair of the Messenger of Allah (ﷺ) was thicker than your hair and these were more fine (than yours)
Reference: Muslim 743