Sayyiduna Ali (may Allah be pleased with him) called for water for ablution, and a vessel containing water was brought. He mentioned the hadith, and in it is: he poured water three times with his right hand onto his right foot, then washed it with his left hand; then he poured water with his right hand onto his left foot and washed it with his left hand. Then he said: "This is the ablution of the Messenger of Allah (peace and blessings be upon him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 351