Is an injured employee entitled to claim the monthly bonus he regularly received, which the company refuses to pay on the grounds that he has stopped working, especially given that the labor law in his country stipulates the continued payment of his full wage to an injured employee, and that this bonus was part of his wage, as documented in his payroll statements?

If the questioner has contracted with the company on terms that violate custom, then the company is bound by what has been contracted upon, not by what custom dictates, as custom is considered only when there is no explicit statement to the contrary. The presence of a condition necessitates acting upon it. The pressure of reality and need does not affect the contract as long as choice is available. So, if the contract stipulates that commission is not due except upon work, then the questioner has no right to it unless the condition is met.