The month of Ramadhan [is that] in which was revealed the Quran, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the crescent of] the month,[1] let him fast it; and whoever is ill or on a journey – then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful.

Quran (2:185)