Sayyiduna Amr bin Abasah al-Sulami (may Allah be pleased with him) mentioned a long hadith about his coming to the Prophet (peace and blessings be upon him) in Makkah and then coming to him in Madinah. He says: I said: O Messenger of Allah, what is ablution? Tell me about it. He (peace and blessings be upon him) said: "When a person brings his water near, then rinses his mouth and draws water into his nose, then blows it out, the sins of his mouth and nostrils leave with the water. Then, when he washes his face as Allah commanded him, the sins of his face leave from the edges of his beard with the water. Then he washes his arms including the elbows, and the sins of his hands leave from his fingertips with the water. Then he wipes his head, and the sins of his head leave from the ends of his hair with the water. Then he washes his feet up to the ankles, and the sins of his feet leave from his toes with the water. Then, if he stands and prays, praising Allah Almighty and extolling Him, glorifying Him as He deserves, and empties his heart for Allah, he becomes as free of his sins as on the day his mother gave birth to him."
(b) It is narrated from Ikrimah: "Then he washes his feet up to the ankles as Allah commanded him." Yahya bin Abi Kathir is not mentioned in its chain.
(c) Muhammad bin Ishaq bin Khuzaymah (may Allah have mercy on him) narrated it from Muhammad bin Yahya al-Dhuhli from Abu al-Walid, and used it as evidence that washing the feet is obligatory.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 382