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).
Reference: Sahih Muslim 2261 d
In-book reference: Book 42, Hadith 4
USC-MSA web (English) reference(deprecated numbering scheme): Book 29, Hadith 5616