Musannaf Ibn Abi Shayba 1:1661

Ibn ‘Ulayyah narrated to us, from Ayyub, from Abu Qilabah, from a man from Banu ‘Amir, from Abu Dharr, from the Prophet (peace be upon him), who said: "The pure earth is a means of purification, as long as water is not found, even if it be for ten years. So when you find water, then touch it to your skin."