The Messenger of Allah (may Allah's peace and blessings be upon him) used to pour water over his head thrice

Abu Ja‘far Muhammad ibn ‘Ali and his father were visiting the noble Companion Jābir ibn ‘Abdullāh (may Allah be pleased with him) and he had some people with him. One of the men asked Jābir how much water would be sufficient for the ritual bath, and he replied: "One Sā‘ of water is sufficient for you." Al-Hasan ibn Muhammad ibn al-Hanafiyyah, who was one of those people sitting with Jābir, said that this amount was not sufficient for him to take a ritual bath.

So, Jābir said that it was sufficient for someone who had more hair than him, and who was better than him, and therefore more careful than him regarding his purity and his religion (referring to the Prophet (may Allah's peace and blessings be upon him). This is meant to urge Muslims to follow the Sunnah and avoid wasting water while taking a ritual bath. Then Jābir led them in prayer.