The Messenger of Allah ﷺ saw some people (performing ablution) while their heels were dry. He then said : Woe to the heels because of Hell. Perform the ablution in full.  

أَنَّ رَسُولَ اللَّهِ ﷺ رَأَى قَوْمًا وَأَعْقَابُهُمْ تَلُوحُ فَقَالَ وَيْلٌ لِلأَعْقَابِ مِنَ النَّارِ أَسْبِغُوا الْوُضُوءَ