‘Abdullāh ibn ‘Amr (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Anyone who practices medicine although he is not known to have learned medicine is liable (to compensate any damage)."
Anyone who claims to know medicine while he has neither knowledge nor experience in it and thus deludes people into receiving his treatment is responsible for the damages that he causes to them. In this respect, he has transgressed by cheating people and practicing something that he did not master. No difference is reported on the fact that if someone treats another and commits a transgression in the treatment process whereby the sick person who receives treatment is damaged, the treating person is responsible for the damage. The same thing applies to anyone who practices a science or a job of which he has no knowledge; he is a transgressor. If damage results from his practice, he is required to pay blood money for it. However, no retribution is to be inflicted on him, for he handled the sick person with his permission.