Muhammad bin Ziyadah says that once Hazrat Abu Hurairah (may Allah be pleased with him) saw a man who had left his heels dry. Hazrat Abu Hurairah (may Allah be pleased with him) said, "Perform ablution thoroughly, for I heard the Noble Prophet (peace and blessings be upon him) say: 'Woe to the heels from the fire of Hell.'"
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 9265