Sahih Bukhari | Volume 1 | Hadith Number 57
Narrated by 'Abdullah bin 'Amr
Once the Prophet 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 addressed us in a loud voice and said twice or thrice: "Save your heels from the fire."