Sayyiduna Ibn Abbas (may Allah be pleased with them both) said to Ata' bin Yasar: Shall I not show you the ablution of the Messenger of Allah (peace and blessings be upon him)? Then he performed ablution (washing each part) once, and washed his feet while there were sandals on his feet.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 348