Al-Baqarah 2:184

For days (ayyāman, ‘days’, is in the accusative as the object of al-siyām, ‘the fast’, or of an implied yasūmū, ‘he fasts’) numbered, few or specific in number, that is, those of Ramadān, as will be mentioned below; God has specified a small number as a way of facilitating matters for those under the obligation; and if any of you, during the month, be sick, or be on a journey, in which prayers are shortened, or if one is strained by the fast in both cases and breaks it, then a number of other days, equal to the ones during which he broke his fast — let him fast them instead; and for those who are, not, able to do it, [to fast] on account of old age or chronic illness, a redemption: which is, the feeding of a poor man, with about the same amount one consumes in a given day, that is, one mudd measure of the principal food of that town each day (a variant reading has [genitive] fidyatin as an explicative clause. It is also said that the [lā] negation of the verb [yutīqūnahu] is not actually implied, because at the very beginning of Islam, they could choose between fasting or offering the redemption; but later on this was abrogated by fixing the Fast [as an obligation], where God says, So let those of you, who are present at the month, fast it [Q. 2:185]: Ibn ‘Abbās said [by way of qualification] ‘Except for the pregnant one and the one breastfeeding, if they break their fast out of concern for the child; in the case of these two, the verse remains valid and has not been abrogated’). For him who volunteers good, by offering more than the minimum amount mentioned for the redemption; that, volunteering, is good for him; but that you should fast (wa-an tasūmū is the subject) is better for you (khayrun lakum is its predicate), than breaking the fast and paying the redemption, if you but knew, that this is better for you, then do it.