SAHIH BUKHARI

Volume 1, Book 4, Number 164:

Narrated by 'Abdullah bin 'Amr
The Prophet remained behind us on a journey. He joined us while we were performing ablution for the 'Asr prayer which was over-due and we were just passing wet hands over our feet (not washing them thoroughly) so he addressed us in a loud voice saying twice orthriae, "Save your heels from the fire."