and he may even advance payment; however, should you accept from that same genus an article of higher quality, the deal slips into the forbidden practice of bayʿ al-ḍamān—the “sale of liability”—thereby shifting the risk back onto the one who was already obliged. This ruling extends to every commodity that Islamic law allows to be exchanged only when it is hand-to-hand and equal for equal. Grasp this principle well and apply it to analogous cases.