[Machine] The Messenger of Allah ﷺ saw a group of people sitting on their heels, with the water not reaching the place of a dirham or the size of a fingernail. He said, "Woe to the heels from the Fire." And one of them was seen repeatedly performing ablution when he saw a spot on his heel that was not washed. This, if authenticated, is something they chose for themselves, and it is possible that he meant only to redo the ablution for that specific spot.  

رَأَى رَسُولُ اللهِ ﷺ قَوْمًا عَلَى أَعْقَابِ أَحَدِهِمْ مِثْلُ مَوْضِعِ الدِّرْهَمِ أَوْ مِثْلُ مَوْضِعِ الظُّفُرِ لَمْ يُصِبْهُ الْمَاءُ قَالَ فَجَعَلَ يَقُولُ وَيْلٌ لِلْأَعْقَابِ مِنَ النَّارِ قَالَ وَكَانَ أَحَدُهُمْ يَنْظُرُ أَنَّهُ إِذَا رَأَى بِعَقِبِهِ مَوْضِعًا لَمْ يصِبْهُ الْمَاءُ أَعَادَ وُضُوءَهُ وَهَذَا إِنْ صَحَّ فَشَيْءٌ اخْتَارُوهُ لِأَنْفُسِهِمْ وَقَدْ يُحْتَمَلُ أَنْ يرِيدَ بِهِ إِعَادَةَ وُضُوءِ ذَلِكَ الْمَوْضِعِ فَقَطْ