Musnad Ahmad 289:16

'Abd al-Rahman ibn Mahdi and Bahz—the meaning is the same—said: Shu'bah narrated to us, from Ya'la ibn 'Ata', (Bahz said in his narration: He said: Ya'la ibn 'Ata' informed me, he said: I heard Waki' ibn Hudus, from his paternal uncle Abu Razin, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The dream of the believer is one part of forty parts of prophethood. It remains upon the foot of a bird as long as it is not spoken of; but when it is spoken of, it falls." And I think he said: "And he should not speak of it except to a loved one or a person of intelligence."