As a veterinarian, is treating a black dog forbidden because it is a devil?

The basic principle is that treating dogs is permissible, unless the treatment aids in an unlawful possession, in which case it is prohibited as a deterrent to the unlawful act. Therefore, it is permissible to treat a dog whose possession is allowed, such as a hunting dog or a guard dog. However, for a dog whose possession is forbidden, treating it and caring for it is a means to possess what is prohibited, and means are subject to the rulings of their ends.

As for the black dog, its possession is forbidden according to a group of scholars, and the Prophet, peace and blessings be upon him, commanded its killing. Consequently, treating a black dog is not permissible if it is known or highly probable that it will be possessed.