Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "Would you like me to tell you (the manner) in which the Messenger of Allah (peace and blessings be upon him) used to perform ablution?" Then he (may Allah be pleased with him) called for a vessel of water and described the ablution of the Prophet (peace and blessings be upon him). In it, it says: Then he took a handful of water and sprinkled it on his right foot while the sandal was on the foot, then wiped over the top and the bottom of the foot, then did the same with the left foot.
This is the most authentic hadith narrated from the Prophet (peace and blessings be upon him) on this (point), and it agrees with the narration of the group.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 347