From Sahih Muslim (Hadith 740):
Jubair b. Mut'im reported:The people contended amongst themselves in the presence of the Messenger of Allah (ﷺ) with regard to bathing. Some of them said: We wash our heads like this and this. Upon this the Messenger (ﷺ) said: As for me I pour three handfuls of water upon my head
Reference: Muslim 740