Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that a man performed ablution and came to the service of the Prophet (peace and blessings be upon him), and he had left a spot the size of a fingernail dry on the upper part of his foot. So the Prophet (peace and blessings be upon him) said to him: "Go back and perform your ablution properly." Imam Abu Bakr (may Allah have mercy on him) says that Ahmad bin Abdur Rahman bin Wahb narrated to us, he says that my uncle narrated this hadith to us in the same way.