Chapter on Usury (Riba)
Man Lā Yaḥḍuruh al-Faqīh|Volume 3|Book 2|Chapter 27
وَ سَأَلَ سَمَاعَةُ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنْ بَيْعِ اَلْحَيَوَانِ اِثْنَيْنِ بِوَاحِدٍ - فَقَالَ "إِذَا سَمَّيْتَ اَلسِّنَّ فَلاَ بَأْسَ".
Sama'ah asked Abu Abdullah عليه السلام about selling two animals for one. Imam عليه السلام said: "If you specify their age, then there is no harm."
- Ṣaḥīḥ al-Faqīh, p. 245