Sahih al-Bukhari #343

Narrated Al-A`mash: Shaqiq said, "While I was sitting with `Abdullah and Abu Musa Al-Ash`ari, the latter asked the former, 'If a person becomes Junub and does not find water for one month, can he perform Tayammum and offer his prayer?' (He applied in the negative). Abu Musa said, 'What do you say about this verse from Sura "Al-Ma'ida": When you do not find water then perform Tayammum with clean earth? `Abdullah replied, 'If we allowed it then they would probably perform Tayammum with clean earth even if water were available but cold.' I said to Shaqiq, 'You then disliked to perform Tayammum because of this?' Shaqiq said, 'Yes.' (Shaqiq added), "Abu Musa said, 'Haven't you heard the statement of `Ammar to `Umar? He said: I was sent out by Allah's Messenger (ﷺ) for some job and I became Junub and could not find water so I rolled myself over the dust (clean earth) like an animal does, and when I told the Prophet (ﷺ) of that he said, 'Like this would have been sufficient.' The Prophet (ﷺ) (saying so) lightly stroked the earth with his hand once and blew it off, then passed his (left) hand over the back of his right hand or his (right) hand over the back of his left hand and then passed them over his face.' So `Abdullah said to Abu- Musa, 'Don't you know that `Umar was not satisfied with `Ammar's statement?' " Narrated Shaqiq: While I was with `Abdullah and Abu Musa, the latter said to the former, "Haven't you heard the statement of `Ammar to `Umar? He said, "Allah's Messenger (ﷺ) sent you and me out and I became Junub and rolled myself in the dust (clean earth) (for Tayammum). When we came to Allah's Apostle I told him about it and he said, 'This would have been sufficient,' passing his hands over his face and the backs of his hands once only.' "