Is it permissible for me to take the discount that the supplier grants me on the price of devices I acquire for others, knowing that he gives me the general price and then discounts it for me due to my personal relationship with him?

Ahmad said: If one gives a garment to a man to sell, and he sells it, and the buyer gifts him a handkerchief, then the handkerchief belongs to the owner of the garment. This is because the gift of the handkerchief was occasioned by the sale, making the handkerchief an increase in the price. An increase in the session of the contract is appended to it. Therefore, it is not permissible to take a commission except with the explicit permission of the principal.