Chapter on Usury (Riba)
Man Lā Yaḥḍuruh al-Faqīh|Volume 3|Book 2|Chapter 27
وَ رَوَى أَبُو بَصِيرٍ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ قَالَ: "اَلْحِنْطَةُ وَ اَلشَّعِيرُ رَأْسٌ بِرَأْسٍ لاَ يُزَادُ وَاحِدٌ مِنْهُمَا عَلَى اَلْآخَرِ".
Abu Basir narrated from Abu Abdullah عليه السلام, who said: "Wheat and barley should be exchanged one for one, and neither of them should exceed the other."
- Ṣaḥīḥ al-Faqīh, p. 245