Sunan An-Nasai, Chapter: The Book of Purification

from his father, that man asked Umar bin Al-Khattab about Tayammum and he did not know what to say. 'Ammar said: "Do you remember when we were on a campaign, and I became Junub and rolled in the dust, then I came to the Prophet (saw) and he said: 'This would have been sufficient.'" (One of the narrators) Shu'bah struck his hands on his knees and blew into his hands, then he wiped his face and palms with them once. (Sahih)