Amr bin Shu'ayb narrates from his father, from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "Whoever practises medicine (treatment) without knowledge and causes harm to the patient, he is liable for it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسامة / 16530