Musnad Ahmad 648:20

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from al-Hakam, from Dharr, from Ibn ‘Abd al-Rahman ibn Abza, from his father, that a man came to ‘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, O Commander of the Faithful, when you and I were in a military expedition and we became in a state of major ritual impurity, and we did not find water? As for you, you did not pray, but as for me, I rolled in the dust and prayed. When we came to the Prophet, may Allah bless him and grant him peace, and I mentioned that to him, he said: 'It would have been sufficient for you.'" And the Prophet, may Allah bless him and grant him peace, struck the ground with his hand, then blew into it, and wiped his face and his palms with it.