Beautiful Hadith is about Wudu

Narrated `Abdullah bin `Amr RA: Once the Prophet (peace be upon him) 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 (peace be upon him) addressed us in a loud voice and said twice or thrice: "Save your heels from the fire." (Bukhari - Vol. 1, Book 3, Hadith 57)