Musnad Ahmad 32:461

Hashim narrated to us, Sulayman narrated to us, from Thabit, from Anas, who said: "When the Prophet, peace and blessings of Allah be upon him, would pray the morning prayer, the servants of the people of Medina would come with their vessels containing water. There was not a vessel brought to him except that he would dip his hand into it. Sometimes they would come to him on a cold morning, and he would still dip his hand into it."