What should I do right after a bad dream in Islam?

Seek refuge in Allah from Shaytan and the evil of the dream, spit lightly to your left 3 times, turn onto the other side, and do not tell anyone. Praying is added in Muslim 2263a. The Prophet ﷺ said that done this way the dream will not harm you (Bukhari 6985).

Does 'spit' in the hadith mean literally spitting?

The English translations say spit. Commentators explain it as a light dry blow with perhaps a trace of moisture, a gesture of disgust at Shaytan's suggestion and not an act aimed at anything. Nobody is asked to spit on the floor or on a person.

Can I ever tell a bad dream to a scholar to have it interpreted?

The hadith say to tell it to no one, and they say it will not harm you if you do not. If a dream is troubling your sleep or health, speak to a doctor about that. Interpreting a disliked dream is not what the Sunnah asks of you; dismissing it is.

What to do after a good or a bad dream (the Sunnah)

There is no ritual in Islamic dream interpretation that comes with so clear a promise: do these things, and the dream will not harm you. The Prophet ﷺ said it in nearly those words, and two men who had been made ill by frightening dreams, the Companion Abu Qatada and Abu Salama, who learned it from him, said that once they heard it the dreams stopped troubling them. So this is the place to start when a dream has unsettled you, before you look anything up.

The routine for a dream you dislike, with its sources

Different narrations preserve different parts of the advice, and put together they make one short routine. This table says where each step is found, so you can check it.

Step	What to do	Where it is
1	Seek refuge in Allah from Shaytan and from the evil of the dream	Bukhari 7005, Bukhari 7044
2	Spit lightly to your left, 3 times	Muslim 2261d, Muslim 2262, Bukhari 7044
3	Turn over onto the other side from the one you were lying on	Muslim 2262
4	Tell no one	Bukhari 6985, Muslim 2261f
5	Get up and pray, if you wish	Muslim 2263a, and Bukhari 7017 in the words Ibn Sirin passes on

The promise attached to all this is in Bukhari 6985, where the Prophet ﷺ says of the dream that you should not mention it to anyone, "for it will not harm him". Abu Salama's story shows what it meant in practice. He used to see dreams that weighed on him "more heavily than a mountain", until he heard this hadith from Abu Qatada. After that, he said, he no longer cared about them (Muslim 2261d; Bukhari 7044 has Abu Qatada saying the same had happened to him).

Two small points on the wording. The translations say "spit" for what scholars commonly explain as a light, dry blow, perhaps with a trace of moisture, toward your left. It is a gesture of disgust, and nobody is asked to spit at anything. And "turn over" in Muslim 2262 is as literal as it sounds: change the side you are lying on. Commentators find a psychological wisdom in it, a small physical break that interrupts the dream's hold. That explanation is theirs and is reasonable, but the hadith simply gives the instruction.

If the dream was good

For a dream you like, the Prophet ﷺ said it is from Allah, so you should thank Him for it (Bukhari 6985). Then comes the part people ask about: whom to tell. Bukhari 6985 says you may narrate it, while Bukhari 7044 and Muslim 2261f say you should tell it only to someone you love. Commentators generally read the general wording in the light of the specific: tell it to a loved one, not to everyone.

There is a second reason, and it is older. When the boy Yusuf told his father his dream, Yaqub answered: do not relate your vision to your brothers, or they will plot against you (Qur'an 12:5). A good dream, spoken in the wrong company, can draw envy.

One more hadith deserves care. Abu Razin reports the Prophet ﷺ saying that a believer's dream sits, as it were, on the leg of a bird as long as it is not spoken of, and when it is spoken of it falls (Tirmidhi 2279; al-Tirmidhi calls it hasan sahih, and al-Albani and Ahmad Shakir grade it sahih). In another version the narrator adds that it should be told only to "an intelligent one or a beloved one" (Tirmidhi 2278). Commentators have understood the image as saying a dream tends to come to pass as it is first interpreted, which is why who interprets it matters. The practical result is the same as the other hadith: be choosy about the listener.

Why not telling is part of the cure

The oddest part of the Sunnah's advice, to a modern reader, is that you should not talk it out. We think the reason is easy to see once you read the stories. A man comes to the Prophet ﷺ and says he saw his own head cut off and rolling away and himself chasing it. The Prophet ﷺ laughed and told him not to report to people the "play of Shaytan" with him in his sleep (Muslim 2268c, Muslim 2268e). He did not interpret it. The gesture is a refusal to give the dream a hearing.

Our own observation, and not a text: retelling a frightening dream makes it a story, and a story gets elaborated, compared with other people's, and carried into the next night. The Sunnah's version stops the story before it starts. If something about it keeps coming back, that is a matter for a different page: recurring nightmares and when to see a doctor.

What not to do with a dream

Do not claim a dream you did not have. The Prophet ﷺ called it the worst of lies and said whoever claims one will be told to tie a knot between two barley grains, which he cannot do (Bukhari 7043, Bukhari 7042). The severity shows how seriously true dreams are taken.
Do not make a decision on it. A dream does not create a ruling or cancel one, as we explain in can dreams be true in Islam.
Do not interpret someone else's frightening dream for them. Let it be dismissed.

All of this assumes you have already sorted the dream into one of the three kinds. If you want the whole routine as something you can tick off each night, the bedtime checklist puts it, and the manners before sleep that protect you from needing it, in one place.