Abu Hurayrah saw a man whose feet had patches left dry. He said, "Perform ablution properly, for I heard the Messenger of Allah ﷺ say, 'Woe to the heels from the Fire.'"
حدثنا عفان قال حدثنا حماد قال
أن أبا هريرة رأى رجلا مبقع الرجلين فقال أحسنوا الوضوء فإني سمعت رسول الله ﷺ يقول ويل للأعقاب من النار
Its isnad is sahih. Bukhari related it in 1/53, in the chapter on wudu, on washing the heels, and Muslim in 1/214, number 242, in the chapter on purification, on the obligation of washing the feet, and Abu Dawud in 1/24, number 97, in the chapter on purification, on performing wudu thoroughly, and Tirmidhi in 1/58, number 41, in the chapter on purification, on what has been said regarding "woe to the heels from the Fire," and he said, hasan sahih.