Hadith: Allah is the Physician. You are only a kind man. The one who heals it is the One who created it

عن أبي رَمْثة رضي الله عنه أنَّه قال للنبي صلى الله عليه وسلم : أَرِني هذا الذي بظهرك، فإنِّي رجلٌ طبيبٌ، قال: «اللهُ الطبيبُ، بل أنت رجلٌ رَفِيقٌ، طبيبُها الذي خلقَها».
[صحيح] - [رواه أبو داود وأحمد]

Abu Ramthah (may Allah be pleased with him) reported that he said to the Prophet (may Allah’s peace and blessings be upon him): "Show me this thing on your back (to treat it), for I am a physician." The Prophet (may Allah's peace and blessings be upon him) replied: "Allah is the Physician. You are only a kind man. The one who heals it is the One who created it.”
[Authentic hadith] - [Narrated by Abu Daoud - Narrated by Ahmad]

Explanation

Abu Ramthah was a physician. When he saw the mark of prophet-hood protruding between the shoulder blades of the Prophet (may Allah's peace and blessings be upon him), he thought that it was a lump formed by waste substances. So, he asked the Prophet (may Allah's peace and blessings be upon him) to let him treat it because he was a physician. The Prophet (may Allah's peace and blessings be upon him) replied that Allah is the Physician, i.e. he is the true healer who treats the disease with the medicine that cures it. His words: “You are only a kind man” mean that you are only kind and gentle to the patient. That is because a physician is the one who is knowledgeable of the true nature of the disease and medicine, and he is the one who is able to grant health and recovery. No one could do this but Allah.