What is the ruling on working in non-Islamic slaughterhouses, and what about the salary earned from this work?

It is not permissible to work in slaughterhouses that do not adhere to the Islamic regulations for slaughtering, as this involves cooperating in sin and deceiving people. If a Muslim worked there out of ignorance, there is no blame upon him for the wages he received. However, if he knew of its prohibition, then the money he took is not lawful for him, and he must disburse its equivalent amount for the benefit of Muslims, the poor, and the needy, in order to clear his conscience.