Musannaf Ibn Abi Shayba 23:199

Al-Ala’ ibn Mansur narrated to us, he said: Yahya ibn Hamza narrated to me, from Burayd ibn Ubaydah, from Abu Ubayd Allah, from Awf ibn Malik al-Ashja’i, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Dreams are of three types: among them is a frightening from Satan to cause grief to the son of Adam; among them is that which a person speaks to himself about while awake, so he sees it in his sleep; and among them is a part of forty-six parts of prophethood."