Al-Baqarah 2:184

Ayyaman maAAdoodatin faman kanaminkum mareedan aw AAala safarin faAAiddatun minayyamin okhara waAAala allatheena yuteeqoonahufidyatun taAAamu miskeenin faman tatawwaAAakhayran fahuwa khayrun lahu waan tasoomoo khayrun lakum inkuntum taAAlamoon

[Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] - then an equal number of other days [are to be made up]. And upon those who are able [to fast, but with hardship] - a ransom [as substitute] of feeding a poor person [each day]. And whoever volunteers good [i.e., excess] - it is better for him. But to fast is best for you, if you only knew.

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.