إِنَّ الرِّبَا وَإِنْ كَثُرَ فَإِنَّ عَاقِبَتَهُ تَصِيرُ إِلَى قُلٍّ
Translation: Even if usury grows large, its eventual outcome leads to diminution.
Source: ابن ماجه
الرِّبَا denotes usury or interest in the prohibited sense. The narration contrasts outward increase with an ultimately diminished result. وَإِنْ كَثُرَ means “even if it becomes abundant,” while عَاقِبَتَهُ means “its outcome.” The teaching cautions against being deceived by apparent financial growth that relies on an unlawful practice.
كَثُرَ is a past-tense verb meaning “became plentiful.” In فَإِنَّ عَاقِبَتَهُ, عَاقِبَتَ is the accusative noun of inna, and ـهُ points back to ribā. تَصِيرُ means “becomes or leads to,” and إِلَى قُلٍّ means “toward reduction.” The qāf of قُلٍّ bears ḍammah.
An attractive promised return does not settle whether a transaction is lawful. One should examine its substance and rights. The narration does not make all trade forbidden or identify every financial loss as punishment.