What is the ruling on the increase (bonus) to the agreed-upon salary, stipulated upon exceeding the daily sales average or selling products nearing their expiration date?

If the increase in wages is an independent bonus to encourage the worker, then it is permissible and considered a form of 'ja'l' (payment for a specific task or achievement).

However, if the increase is part of the salary, this leads to 'jahala' (uncertainty) in the wage. One of the conditions for a valid 'ijara' (lease or hiring contract) is that the wage must be known, either as a fixed amount or a percentage of the profit. Combining a fixed amount with a percentage is, according to the preponderant opinion, impermissible.