Fasting is obligatory for every muslem with shahadah mature and normal healthy,you should not be sick.
Anyway if you're sick the penalty is you have to feed sixty muslems the whole months of Ramadhan for you to get the rewards of fasting.
GOD says in Hadith Al qudusi( fasting belongs to me and only GOD knows the payment of fasting)and this is the main logic behind why muslems have to fast 30 days of the whole months of Ramadhan like the Quran says"ayaamul ma aduudat"that days are countable just 30days and then we go the celebration of iddi Al adhuha.
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