Abu Qatada reported Allah's Messenger (ﷺ) as saying:
A good vision is from Allah and a bad dream (hulm) is from the satan; so if one of you sees anything (in a dream) which he dislikes, he should spit on his left side thrice and seek refuge with Allah from its evil, and then it will never harm him. Abu Salama said: I used to see dreams weighing more heavily upon me than a mountain; but since I heard this hadith I don't care for it (its burden). (ID)
Reference (ID): Sahih Muslim 2261 d (ID)
In-book reference (ID): Book 42, Hadith 4 (ID)
USC-MSA web (English) reference(deprecated numbering scheme): Book 29, Hadith 5616 (ID)