Musnad Ahmad 289:14

Bahz narrated to us, he said: Shu'bah narrated to us, he said: Ya'la ibn 'Ata informed me, he said: I heard Waki' ibn 'Adus narrating from his uncle, Abu Razin, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The dream of a Muslim is one part of forty parts of prophethood. It is upon the leg of a bird as long as he does not speak of it; but if he speaks of it, it falls." He said: I think he said: "He should not speak of it except to a loved one or a person of intellect."