Sahih Al Bukhari – Book of Medicine
Volumn 007, Book 071, Hadith Number 643.
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Narated By 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."