Is it permissible for a Muslim veterinarian to cremate dog carcasses for his European clients to obtain their ashes?

It is not permissible for anyone to assist in disobedience to Allah. Whoever assists in it is a partner in sin. Burning an animal after its death is permissible if it serves a benefit, such as removing the harm of odor. However, if there is no benefit and the harm is evident, then it is not permissible. Burning dogs after their death to obtain their ashes is forbidden, due to the strong presumption that this act is done for forbidden and foolish purposes. Therefore, building a furnace for this purpose is considered assisting in sin and transgression.