Sahih al-Bukhari 163Book 4, Hadith 29
حَدَّثَنَا مُوسَى، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ أَبِي بِشْرٍ، عَنْ يُوسُفَ بْنِ مَاهَكَ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، قَالَ تَخَلَّفَ النَّبِيُّ صلى الله عليه وسلم عَنَّا فِي سَفْرَةٍ سَافَرْنَاهَا، فَأَدْرَكَنَا وَقَدْ أَرْهَقْنَا الْعَصْرَ، فَجَعَلْنَا نَتَوَضَّأُ وَنَمْسَحُ عَلَى أَرْجُلِنَا، فَنَادَى بِأَعْلَى صَوْتِهِ " وَيْلٌ لِلأَعْقَابِ مِنَ النَّارِ ". مَرَّتَيْنِ أَوْ ثَلاَثًا.
The Prophet (ﷺ) remained behind us on a journey. He joined us while we were performing ablution for the `Asr prayer which was overdue and we were just passing wet hands over our feet (not washing them thoroughly) so he addressed us in a loud voice saying twice , "Save your heels from the fire."