Ablutions (Wudu')

Bukhari :: Book 1 :: Volume 4 :: Hadith 164

Narrated '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."