Tafsir of An-Nur 24:7

(And the fifth [testimony]) meaning: the fifth testimony in addition to the four preceding ones—that is, the one that renders them five by being joined to them, and which is singled out despite being a testimony like them, due to its independence in import and its strength in conveying what is intended by the testimony: the verification of the report and the manifestation of truthfulness. This is a subject (mubtada') whose predicate is the saying of the Exalted: (that the curse of Allah be upon him if he were among the liars) in that which he accused her of regarding adultery.