Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "Shall I not show you the ablution of the Prophet (peace and blessings be upon him)?" Then he described the manner of ablution: he washed his hands once, rinsed his mouth once, sniffed water into his nose once, washed his face once, washed his forearms once, wiped his head only once, and washed his feet once. Then he said: "This is the ablution of the Prophet (peace and blessings be upon him)."
This chain is sahih (authentic).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 317