Musnad Ahmad 289:1

Hashim narrated to us, he said: Ya'la ibn 'Ata' informed us, from Waki' ibn 'Adus, from his uncle Abu Razin, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "The vision is upon the leg of a bird, as long as it is not interpreted; but if it is interpreted, it falls." He said: "And the vision is a part of forty-six parts of prophethood." He said: And I think he said: "Do not relate it except to a loving one, or one of sound judgment."