Sahih Bukhari
Interpretation of Dreams
Volume: 009 / Book Number: 087 / Hadith Number: 115
Narrated Abu Qatada:
The Prophet said, "A good dream that comes true is from Allah, and a bad dream is from Satan, so if anyone of you sees a bad dream, he should seek refuge with Allah from Satan and should spit on the left, for the bad dream will not harm him."