Sahih Muslim Book 3, Hadith Number 638.

Chapter : The desirability of pouring water thrice on the head and other parts (of the body).

Jubair b. Mut’im reported: The people contended amongst themselves in the presence of the Messenger of Allah (may peace be upon him) with regard to bathing. Some of them said: We wash our heads like this and this. Upon this the Messenger (may peace be upon him) said: As for me I pour three handfuls of water upon my head.