A man came to 'Umar bin khattab and said: "I became impure following sexual emission and cannot find any water." 'Umar said to him: "Do not pray." But 'Ammar bin Yasir said: "Do you not remember, O Commander of the Believers, when you and I were on a military expedition and we became sexually impure and could not find water? As for you, you did not pray, but I rolled in the dust and then prayed. When I came to the Prophet and told him what had happened, he said: 'It would have been enough for you (to do this).' (Then demonstrating) the Prophet struck the ground with his hands, then blew on hem, and wiped his face and palms with them."