Musnad Ahmad 30:2007

Hawdha ibn Khalifah narrated to us, 'Awf narrated to us, from Muhammad, from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace, who said: "Dreams are of three types: glad tidings from Allah, the inner talk of the self, and frightening from Satan. So if one of you sees a dream that pleases him, let him relate it if he wishes. And if he sees something he dislikes, let him not relate it to anyone, and let him stand up and pray."