Fasting is prescribed to you as it was prescribed to those before you

O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous.

[Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] - then an equal number of 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 excess - it is better for him. But to fast is best for you, if you only knew.

(Quran: Surat Al-Baqarah 183, 184)