Musnad Abu Ya'la al-Mawsili 105:6

Al-Qawariri narrated to us, Yazid bin Zuray' narrated to us, Shu'bah narrated to us, from al-Hakam, from Dharr, from Abd al-Rahman bin Abza, from his father, from Umar bin al-Khattab and Ammar bin Yasir, who said: A man asked Umar and said: "I became in a state of major ritual impurity (janabah) and did not find water." Umar said: "Do not pray." Ammar said: "Do you not remember when I and you were in a military expedition during the time of the Messenger of Allah (peace be upon him), and we became in a state of major ritual impurity? As for you, you did not pray, and as for me, I rolled in the dust and prayed. Then I came to the Prophet (peace be upon him) and mentioned that to him." He (the Prophet) said: "It would have been sufficient for you." Then he struck the ground with his hand once, blew into his palms, and wiped his face and his palms.