The Fidyah (Expiation) for breaking the Fast is for the Old and the Ailing
Al-Bukhari reported that `Ata heard Ibn `Abbas recite:
[وَعَلَى الَّذِينَ يُطِيقُونَهُ فِدْيَةٌ طَعَامُ مِسْكِينٍ]
(And as for those who can fast with difficulty, (e.g., an old man), they have (a choice either to fast or) to feed a Miskin (poor person) (for every day).)
Ibn `Abbas then commented, "(This Ayah) was not abrogated, it is for the old man and the old woman who are able to fast with difficulty, but choose instead to feed a poor person for every day (they do not fast).'' Others reported that Sa`id bin Jubayr mentioned this from Ibn `Abbas. So the abrogation here applies to the healthy person, who is not traveling and who has to fast, as Allah said:
[فَمَن شَهِدَ مِنكُمُ الشَّهْرَ فَلْيَصُمْهُ]
(So whoever of you sights (the crescent on the first night of) the month (of Ramadan, i.e., is present at his home), he must observe Sawm (fasting) that month.) (2:185)
As for the old man (and woman) who cannot fast, he is allowed to abstain from fasting and does not have to fast another day instead, because he is not likely to improve and be able to fast other days. So he is required to pay a Fidyah for every day missed. This is the opinion of Ibn `Abbas and several others among the Salaf who read the Ayah:
[وَعَلَى الَّذِينَ يُطِيقُونَهُ]
(And as for those who can fast with difficulty, (e.g., an old man)) to mean those who find it difficult to fast as Ibn Mas`ud stated. This is also the opinion of Al-Bukhari who said, "As for the old man (person) who cannot fast, (he should do like) Anas who, for one or two years after he became old fed some bread and meat to a poor person for each day he did not fast.''
This point, which Al-Bukhari attributed to Anas without a chain of narrators, was collected with a continuous chain of narrators by Abu Ya`la Mawsuli in his Musnad, that Ayyub bin Abu Tamimah said; "Anas could no longer fast. So he made a plate of Tharid (broth, bread and meat) and invited thirty poor persons and fed them.'' The same ruling applies for the pregnant and breast-feeding women if they fear for themselves or their children or fetuses. In this case, they pay the Fidyah and do not have to fast other days in place of the days that they missed.
[شَهْرُ رَمَضَانَ الَّذِى أُنزِلَ فِيهِ الْقُرْآنُ هُدًى لِّلنَّاسِ وَبَيِّنَـتٍ مِّنَ الْهُدَى وَالْفُرْقَانِ فَمَن شَهِدَ مِنكُمُ الشَّهْرَ فَلْيَصُمْهُ وَمَن كَانَ مَرِيضًا أَوْ عَلَى سَفَرٍ فَعِدَّةٌ مِّنْ أَيَّامٍ أُخَرَ يُرِيدُ اللَّهُ بِكُمُ الْيُسْرَ وَلاَ يُرِيدُ بِكُمُ الْعُسْرَ وَلِتُكْمِلُواْ الْعِدَّةَ وَلِتُكَبِّرُواْ اللَّهَ عَلَى مَا هَدَاكُمْ وَلَعَلَّكُمْ تَشْكُرُونَ ]
(185. The month of Ramadan in which was revealed the Qur'an, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). So whoever of you sights (the crescent on the first night of) the month (of Ramadan, i.e., is present at his home), he must observe Sawm (fasting) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasting) must be made up] from other days. Allah intends for you ease, and He does not want to make things difficult for you. (He wants that you) must complete the same number (of days), and that you must magnify Allah [i.e., to say Takbir (Allahu Akbar: Allah is the Most Great)] for having guided you so that you may be grateful to Him.)