He saw the Messenger of Allah ﷺ perform ablution. He described it and said that he wiped his head with fresh water, not with what was left over on his hands, and washed his feet until they were clean.
حدثنا أحمد بن عمرو بن السرح حدثنا ابن وهب عن عمرو بن الحارث أن حبان بن واسع حدثه أن أباه حدثه أنه سمع
أنه رأى رسول الله ﷺ فذكر وضوءه وقال ومسح رأسه بماء غير فضل يديه وغسل رجليه حتى أنقاهما
Ahmad bin AmrTakhrij: Reported by Muslim, in the Book of Purification, Chapter on Another Description of the Manner of Wudu, hadith no. 236, from Ibn Sarh with the same wording. Tirmidhi also reported it, hadith no. 35, and said, "This is a hasan sahih hadith."