เศาะฮีห์อัล-บุคอรี #60

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