Is it permissible to purchase gasoline from another company before the agreed-upon period of five years ends, due to a lower price?

If the company owns the liquid tank on the condition that the customer does not buy from anyone else for a certain period, this is a conditional gift. There is a jurisprudential disagreement regarding the validity of this gift and condition. Some jurists consider the gift invalid if it contains conditions that would invalidate a sale. Others deem the condition void but the contract valid. However, the Malikis, Shafi'is, and Hanbalis, in one view, consider both the contract and the condition void.

A gift does not accept suspension (ta'leeq). Combining a gift contract (donation) with a sales contract (exchange) is not permissible in Islamic law, due to the Prophet's (peace be upon him) prohibition of combining a loan and a sale. This includes any donation combined with a sale or lease.

However, if the company allows the beneficiary to use the tank without owning it, and stipulates that it should only be used for its product, then this is a valid condition that must be fulfilled, based on the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions."

If the tank is built with the intention of transferring ownership, with the condition of preventing purchase from others, then the most preponderant opinion is that both the contract and the condition are void. This is because it is not a pure gift but an exchange. If the condition were invalidated without invalidating the contract, it would be an injustice to the donor. It is also not correct to consider it a gift with an unknown عوض (counter-value/compensation), because a gift with a known عوض becomes a sale. If the عوض is unknown, the gift becomes invalid, and its ruling is that of an invalid sale.