It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with him), the Messenger of Allah (peace and blessings be upon him) said: "Whoever treats (someone) without complete knowledge of medicine, and his practice of medicine is not recognized, then he himself will be responsible (in case of harm)."
Hadith Referenceسلسله احاديث صحيحه / الطب والعيادة / 1621