A Quarter of the Quran, According to One Report

A hadith transmitted through several collections holds that reciting Az-Zalzala is equivalent in reward to reciting one quarter of the entire Quran, part of a small set of similar traditions assigning specific short surahs a fractional value relative to the whole text, Al-Ikhlas most famously reported as equivalent to one third. Hadith scholars examining the chains behind these fractional-value reports generally class at least some of them as weaker than the reports underlying more securely established devotional practices, so the tradition is best treated as a popularly repeated devotional saying rather than a claim resting on the strongest category of hadith evidence.

Independent of that report's reliability, Az-Zalzala's own closing measure, that no act of good or evil however small escapes account (99:7-8), needs no supporting hadith to carry its recognised devotional weight, and classical commentators treat the verse's deliberate use of the smallest conceivable unit of weight as itself sufficient to explain why the surah, brief as it is, occupies an outsized place in popular Islamic ethical teaching regardless of any reported numerical equivalence to a portion of the whole Quran.