Once Messenger of Allah ﷺ remained behind us in a journey. He joined us while we were performing ablution for the ʿAsr prayer which was over-due. We were just passing wet hands over our feet (not washing them properly) so the Prophet ﷺ addressed us in a loud voice and said twice or thrice, "Save your heels from the fire."
تَخَلَّفَ رَسُولُ اللَّهِ ﷺ فِي سَفَرٍ سَافَرْنَاهُ فَأَدْرَكَنَا وَقَدْ أَرْهَقْنَا الصَّلاَةَ صَلاَةَ الْعَصْرِ وَنَحْنُ نَتَوَضَّأُ فَجَعَلْنَا نَمْسَحُ عَلَى أَرْجُلِنَا فَنَادَى بِأَعْلَى صَوْتِهِ وَيْلٌ لِلأَعْقَابِ مِنَ النَّارِ مَرَّتَيْنِ أَوْ ثَلاَثًا