Reports Regarding Dream Categories
Abu Salamah  رحمه الله reported that he used to have dreams that made him ill (from fear or worry) - until he heard Abu Qatadah رضي الله عنه mention that he had the same problem, so Allaah's Messenger صلى الله عليه وسلم told him: "A pleasant (or good, or truthful) dream is from Allaah, and a bad dream is from Shaytaan. When one of you has a good dream (that he likes), let him expect good, and avoid relating it except to those whom he loves. And when he has a dream and dislikes any part of it, let him seek Allaah's protection from its evil and from Shaytaan's evil, and let him lightly spit - three times - on his left side, and avoid relating it to anyone. Indeed, it will then not harm him." 
Abu Sa'eed al-Khudri رضي الله عنه reported that he heard the Prophet صلى الله عليه وسلم say: "When one of you has a dream that he likes - indeed, it is only from Allaah, so let him praise Allaah for it and relate it (to his beloved ones). And if one of you has a dream that he hates - indeed, it is only from Shaytaan, so let him seek Allaah's protection from its evil, and let him not mention it to anyone: it will then not harm him." 
Abu Hurayrah رضي الله عنه reported that the Prophet صلى الله عليه وسلم said: "Dreams are of three categories: a good dream that has glad tidings from Allaah, a terrifying dream from Shaytaan, and a dream about what concerns a person. When one of you has a dream that he dislikes, let him rise from his sleep and pray, and let him not relate it to other people."