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

عن أبي جعفر محمد بن علي بن الحسين بن علي بن أبي طالب أَنَّه كان هو وأبوه عند جابر بن عبد الله، وعنده قوم، فسألوه عن الغسل؟ فقال: صَاعٌ يَكْفِيكَ، فقال رجل: ما يَكْفِينِي، فقال جابر: كان يَكْفِي من هو أَوفَى مِنْكَ شَعْرًا، وخَيرًا مِنكَ -يريد رسول الله- صلى الله عليه وسلم ثُمَّ أَمَّنَا في ثَوبٍ. وفي لفظ: ((كان رسول الله صلى الله عليه وسلم يُفْرِغُ المَاءَ على رَأسِهِ ثَلاَثًا)).
[صحيح] - [الرواية الأولى: متفق عليها الرواية الثانية: رواها مسلم]

Abu Ja‘far Muhammad ibn ‘Ali ibn al-Husayn ibn ‘Ali ibn Abi Tālib reported that he and his father were with Jābir ibn ‘Abdullāh, who had some people sitting with him. They asked him about the ritual bath. He replied: "One Sā‘ of water is sufficient for you." A man said: "It is not sufficient for me." Thereupon, Jābir said: "It was sufficient for someone who had more hair than you and was better than you (meaning the Messenger of Allah (may Allah's peace and blessings be upon him)." Then, Jābir led them in prayer while wearing one garment. In another narration: "The Messenger of Allah (may Allah's peace and blessings be upon him) used to pour water over his head thrice.”
[Authentic hadith] - [Narrated by Muslim - Narrated by Bukhari & Muslim]

Explanation

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.