الكافي 1/4/125/11

11. Ali has narrated from al-Nadr al-Bajali from md ibn Yusuf al-Shashi who has said the following “A boil had grown on my heaps. I sought treament from several physicians and spent money but they said that they knew of no medicine for it. I then wrote a letter to him (the twelfth Imam عليه السلام requesting him to pray. He wrote back to me with his signature, “May Allah grant you good health and place you with us in this life and in the life hereafter.” The narrator has said that before the coming of the Friday the boil was gone and it became like the palm of my hand. I then called one of the physicians and showed him the place of the boil and he said, “We had no knowledge of any medicine to cure it.”