Chapter on Usury (Riba)
Man Lā Yaḥḍuruh al-Faqīh|Volume 3|Book 2|Chapter 27
وَ قَالَ عَلَيْهِ اَلسَّلاَمُ: "أَيُّمَا رَجُلٍ أَدَارَ مَالاً كَثِيراً قَدْ أَكْثَرَ فِيهِ مِنَ اَلرِّبَا فَجَهِلَ ذَلِكَ ثُمَّ عَرَفَهُ بَعْدُ فَأَرَادَ أَنْ يَنْزِعَ ذَلِكَ مِنْهُ فَمَا مَضَى فَلَهُ وَ يَدَعُهُ فِيمَا يَسْتَأْنِفُ ".
Imam عليه السلام said: "If any man manages a large amount of wealth and has excessively engaged in usury unknowingly, then later becomes aware of it and wishes to remove it, what has already passed is permissible for him, but he must refrain from it in the future."
- Ṣaḥīḥ al-Faqīh