Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 643
Narrated Abu Qatada:
I heard the Prophet saying, "A good dream is from Allah, and a bad dream is from Satan. So if anyone of you sees (in a dream) something he dislikes, when he gets up he should blow thrice (on his left side) and seek refuge with Allah from its evil for then it will not harm him."