Abdullah bin al-Harith bin Jaz' al-Zubaydi (may Allah be pleased with him) heard the Messenger of Allah (peace and blessings be upon him) say: "Woe to the heels and the soles of the feet from the Fire!" (Whatever part of the foot remains dry will go into the Fire.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 326