Narrated 'Abdullah bin 'Amr:

The Prophet remained behind us on a journey. He joined us while we were performing ablution for the 'Asr prayer which was over-due and we were just passing wet hands over our feet (not washing them thoroughly) so he addressed us in a loud voice saying twice or thrice, "Save your heels from the fire."

حَدَّثَنَا مُوسَى، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ أَبِي بِشْرٍ، عَنْ يُوسُفَ بْنِ مَاهَكَ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، قَالَ تَخَلَّفَ النَّبِيُّ ﷺ عَنَّا فِي سَفْرَةٍ سَافَرْنَاهَا، فَأَدْرَكَنَا وَقَدْ أَرْهَقْنَا الْعَصْرَ، فَجَعَلْنَا نَتَوَضَّأُ وَنَمْسَحُ عَلَى أَرْجُلِنَا، فَنَادَى بِأَعْلَى صَوْتِهِ " وَيْلٌ لِلأَعْقَابِ مِنَ النَّارِ ". مَرَّتَيْنِ أَوْ ثَلاَثًا.