What is the legal ruling regarding an increase (growth or addition) in the sold item while in the buyer's possession?
Chapter on Selling the Musarrah (Animal with milk retained in udder)
Al-Mughni
Book of Sales
Primary text
If an item sold increases in the buyer's possession, such as by fattening or a similar process, and then decreases back to its original state, there is a possibility that the buyer is liable for that increase. This liability stems from the increase occurring in a guaranteed physical object, resembling an increase in wrongfully possessed property (ghasb). This view is supported by the apparent statement of Imam Ahmad.
Supporting text
Alternatively, the buyer is not liable for the increase because the initial contract did not account for compensation for that addition. Under this view, the increase is considered a trust (amanah) in the buyer's hands; thus, the buyer is only liable if the increase is lost due to negligence (tafrit) or aggression (udwan). If the original item is lost after the increase occurs, the value of the increase is deducted from the total value, and the buyer is liable for the remaining value of the item at the time of loss.