Musnad Abu Ya'la al-Mawsili 42:390

From Abu Sa'id al-Khudri, from the Prophet, may Allah bless him and grant him peace, that he heard him say: "If one of you sees a vision that he likes, then it is from Allah, so let him praise Allah for it and speak of it. And if he sees other than that, from what he dislikes, then it is from Satan, so let him seek refuge from its evil and not mention it to anyone, for it will not harm him."