Abdu Khair, may Allah have mercy on him, says that I once saw Sayyiduna Ali, may Allah be pleased with him, performing ablution. He washed the upper part of his foot and said: If I had not seen the Prophet, peace and blessings be upon him, washing the upper part of his foot, my opinion would have been that the lower part of the foot is more deserving of being washed (because it touches the ground more).