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).
سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ الرُّؤْيَا مِنَ اللَّهِ وَالْحُلْمُ مِنَ الشَّيْطَانِ فَإِذَا رَأَى أَحَدُكُمْ شَيْئًا يَكْرَهُهُ فَلْيَنْفِثْ عَنْ يَسَارِهِ ثَلاَثَ مَرَّاتٍ وَلْيَتَعَوَّذْ بِاللَّهِ مِنْ شَرِّهَا فَإِنَّهَا لَنْ تَضُرَّهُ فَقَالَ إِنْ كُنْتُ لأَرَى الرُّؤْيَا أَثْقَلَ عَلَىَّ مِنْ جَبَلٍ فَمَا هُوَ إِلاَّ أَنْ سَمِعْتُ بِهَذَا الْحَدِيثِ فَمَا أُبَالِيهَا