Musnad Abu Ya'la al-Mawsili 112:4

Al-Hasan ibn Hammad and Hudbah ibn Khalid narrated to us—and the wording is Al-Hasan’s—they said: Hazm ibn Mihran al-Qat’i narrated to us, from Al-Hasan, from Anas, who said: The Messenger of Allah (peace be upon him) went out one day for some of his errands, and with him were people from his companions. They set out traveling, and the time for prayer arrived. The people descended, but they did not find water to perform ablution with. They said: "O Messenger of Allah, we do not find anything to perform ablution with." He saw dislike on the faces of his companions. A man from the people went and brought a vessel with a little water. The Prophet (peace be upon him) took it and performed ablution from it, then he placed his four fingers over the vessel. Then he said to the people: "Come here." The people came and performed ablution until they had reached what they wanted of the ablution. It was said: "How many did the people reach?" He said: "Seventy men, or thereabouts." And the wording is Al-Askari’s.