Sunan An-Nasai, Chapter: The Book of Purification

that Anas mentioned: "The Messenger of Allah (saw) was brought a small vessel (of water) and he performed Wudu." I said: "Did the Messenger of Allah (saw) perform Wudu for every prayer?" He said: "Yes." He said: "What about you?" He said: "We used to pray all the prayers so long as we did not commit Hadath." He said: "And we used to pray all the prayers with (one) Wudu." (Hasan)