Musnad Ahmad 32:1323

Yunus narrated to us, Hazm narrated to us, he said: I heard al-Hasan saying: Anas ibn Malik narrated to us, that the Messenger of Allah (may Allah bless him and grant him peace) 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, but the people did not find water to perform ablution with. They said: "O Messenger of Allah, by Allah, we do not find what we can perform ablution with." And he saw in the faces of his companions a dislike for that. A man from the people went and came with a vessel containing a little water. The Prophet of Allah (may Allah bless him and grant him peace) took it and performed ablution from it. Then he extended his four fingers over the vessel, and then said: "Come, perform ablution." The people performed ablution until they reached what they desired. He said: It was asked, "How many did they reach?" He said: "Seventy, or thereabouts."