Muhammad Sallallahu Alaehe 
Wa AalehiWa Sallam said;
A good dream is from Allah, and a 
bad or evil dream is from Satan.If 
anyone of you has had a bad dream, 
he should spit on his left side 
and seek Refuge with Allah from 
its evil, for then it will not harm him."
Abu Qatada. R.A.
Bukhari Vol. 4 : No. 513