(3) باب مَنْ رَفَعَ صَوْتَهُ بِالْعِلْمِ
Narrated `Abdullah bin `Amr:
Once the Prophet (ﷺ) remained behind us in a journey. He joined us while we were performing ablution for the prayer which was over-due. We were just passing wet hands over our feet (and 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."
Reference: Sahih al-Bukhari 60
In-book reference: Book 3, Hadith 2
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 3, Hadith 57