It was the month of Ramadan in which the Qur’an was first bestowed from on High as a guidance unto Man and a self-evident proof of that guidance, and as a Criterion by which to discern the true from the false; Hence, whoever of you lives to see this month shall fast throughout it; but he that is ill, or on a journey shall instead fast for the same number of other days. Allah wills that you shall have ease, and does not will you to suffer hardship; but He desires that you complete the number of days required, and that you extol Allah for his having guided you aright, and that you render your thanks unto Him.

(translation, with thanks to Muhammad Asad, The Message of the Qur’an)