Abu Dawud Book 34, Hadith Number 4569.
Chapter : On a man who practises medicine without having its knowledge and does harm to the patient.
Narated By Abdullah ibn Amr ibn al-‘As : The Apostle of Allah (PBUH) said: Anyone who practises medicine when he is not known as a practitioner will be held responsible.
Abu Dawud said: This has been transmitted by al-Walid alone. We do not know whether it is sound or not.