Adhab al-qabr, the punishment of the grave, names the suffering a soul may undergo in the interval between death and resurrection, following directly from a failed trial in fitnat al-qabr. Hadith describe it concretely: the grave narrows and crushes, or is filled with fire, or the deceased is beaten with iron rods, sensations reported as real to the soul even though the physical grave itself shows no trace to observers. Reward is described in equally physical terms, a window opened onto paradise or a widened, garden like grave, for a soul that answered its interrogators correctly. Because the doctrine describes events unseen and untestable by the living, its authority rests almost entirely on hadith transmission rather than the Quran, which most exegetes read as alluding to punishment after death only indirectly, in verses about the drowning of Pharaoh's people or the fate of certain earlier nations.
Sunni hadith collections including those of Bukhari and Muslim record the doctrine across multiple chains of transmission, which is part of why it became normative for the traditionalist majority despite its comparatively thin Quranic grounding. Some hadith also describe intermediate outcomes, a grave that is neither wide nor narrow, for believers whose deeds were mixed, underscoring that the punishment and reward described are proportionate rather than uniform.