The doctors told him never to fast, then he recovered five years later
Question

A person had a chronic disease and was advised by doctors not to ever fast. He saw other doctors abroad and was cured by Allah’s grace after five years. For five years he did not fast Ramadaan. What should he do now? Should he make fasting these months up or not?.
Praise be to Allah.If the doctors who gave him this advice were trustworthy Muslims who understand the nature of this sickness, and they told him that there was no hope of recovery, then he does not have to make up the fasts and it is sufficient for him to feed poor people, but he should fast in the future. End quote. 
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) 
Majmoo’ Fataawa wa Maqaalaat Mutanawwi’iah (15/254, 355)