Al-Baqarah 2:184 اياما معدودات فمن كان منكم مريضا او على سفر فعدة من ايام اخر وعلى الذين يطيقونه فدية طعام مسكين فمن تطوع خيرا فهو خير له وان تصوموا خير لكم ان كنتم تعلمون ١٨٤

for days few in number. However, should any one of you be sick or on a journey, then (he should fast) a number of other days (equal to the missed ones); and those who have the strength, (still, they do not opt for fasting,) on them there is a fidyah (compensation), that is, the feeding of a poor person.Then whoever does good voluntarily, that is better for him. However, that you fast is better for you, if you only knew.