ורפא ירפא (משפטים כא:כ)
And the healer will heal.
From this pasuk, a doctor receives permission to heal. (בבא קמא פא)
The chassid Reb Shaya Lebron z’’l related a personal story:
He started experiencing terrible headaches as a young bucher in Belz and consulted with Reb Aharon of Belz zt’’l as to what to do. Reb Aharon advised him to travel to Vienna to see a doctor but warned him not to go to the hospital.
Reb Shaya went to visit the doctor in Vienna, who recommended that he schedule an appointment in the hospital to figure out the cause of his ailments. But Reb Shaya refused to go to the hospital, so the doctor wrote him a prescription for a specific medicine.
When Reb Shaya returned to Belz, he showed the medication to Reb Aharon, who told him to show it to a pharmacist in Belz (Reb Aharon sent many people with various ailments to him) to hear his opinion.
The pharmacist wasn’t pleased with what the doctor in Vienna prescribed and shared his medical opinion. “When you wake up each morning, say Modeh Ani, wash negel vasser, and eat a roll with butter while still in bed. Prepare the roll the night before; this should heal your headaches.”
Reb Shaya returned to Reb Aharon and recounted what the local pharmacist advised.
Reb Aharon shook his head in approval and said that ‘he knows’ and added that Reb Shaya shouldn’t fast any fast days except Yom Kippur.