All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
A person who breaks fasting in Ramadan for some legal reason such as traveling, sickness, menstruation …, is required to make up the days which he did not fast.
Allah says: {… and whoever is ill or on a journey - then an equal number of other days…} [Quran 2:185]
‘Aa’ishah reported that the Prophet said: “We were in menses and we were ordered to make up for the fasting but we were not ordered to make up for the prayers.” [Muslim]
Then, it is not sufficient to feed the poor instead of fasting, since feeding is only required in case of being a patient or old, without possible regaining of ability to fast.
Allah Says (what means): {And upon those who are able [to fast, but with hardship] - a ransom [as substitute] of feeding a poor person [each day].} [Quran 2:184]
Ibn ‘Abbaas said ‘This verse is not abrogated; it is about the old people who cannot observe fasting. So, they are to feed a needy person for each day.’ [Abu Dawood]
It is not permitted to delay making up the fast of the month of Ramadan to the other Ramadan without an Islamically valid excuse. If one delays without having a sound reason, he becomes sinful and is required to make up the days in addition to expiating for missing them, i.e. feeding a poor person for each day.
Abu Hurayrah said regarding the person who delays making up the missed days of Ramadan without any legal reason till the next Ramadan: ‘One has to fast this present Ramadan with people and has also to make up for the missed days and to feed a poor person for each day as well.’
[Ad-Daaraqutni with a good chain of narrators]
The saying of a companion is like a Marfoo’ Hadeeth (traceable in ascending order of Hadeeth to Prophet and this is the ruling according to Muslim scholars.
Thus, it becomes clear that a Muslim has to make up for the missed days (i.e. which he broke fasts) due to legal reasons, and it is not sufficient to expiate as long as he can fast. If it is difficult for him to fast, he can delay from summer to winter, for example. It is normal to face hardship when performing obligations.
Allah knows best.