(27) باب غَسْلِ الرِّجْلَيْنِ وَلاَ يَمْسَحُ عَلَى الْقَدَمَيْنِ
Narrated `Abdullah bin `Amr:
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."
Reference: Sahih al-Bukhari 163
In-book reference: Book 4, Hadith 29
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 4, Hadith 164