He has a kidney disease and the doctor advised him not to fast

No File Exists
Check below answers in case you are looking for other related questions:
What is the sickness which permits a fasting person to break his fast?
Reasons for which one may excused from fasting in Ramadaan

No File Exists
Related Answers:
She needs to keep her weight steady because she wants to have a baby, but she loses weight because of fasting. Can she break the fast in Ramadan?
They put him under anaesthetic when he was fasting, then make him inhale something to wake him up
She is breastfeeding two babies and is afraid that they will be harmed because of fasting
What is the sickness which permits a fasting person to break his fast?
Reasons for which one may excused from fasting in Ramadaan

Recommended answers for you:
Sujood Ul-Sahw if in doubt while praying
Doubts about the obligation to let the beard grow and answers to them
Acceptance of repentance
The meaning of Tawheed and its categories
What are the limits within which parents may interfere in their son’s marriage? Is he sinning if he goes against their wishes?