What is the difference between performing the fast in its proper time and making it up in Ramadan?
Machine translationRead the Arabic original
The questioner : Are there differences between performing the fast and making it up for the month of Ramadan?
The Shaykh : First, making it up is extended to the second Ramadan, whereas performing it in its proper time is restricted; it must be in the month of Ramadan. Second, in the case of performing it in its proper time, expiation is obligatory by scholarly consensus. In the case of making it up, expiation is not obligatory for having intercourse. Third, if a person breaks his fast during the day without an excuse while performing it in its proper time, his fast is invalid, but he is required to abstain for the rest of the day, yes, out of respect for the time. As for making it up, if a person breaks his fast during the day, his fast is invalid, but he is not required to abstain, because there is no sanctity to the time in making it up, since making it up is broad and permissible on all days.
The Shaykh : First, making it up is extended to the second Ramadan, whereas performing it in its proper time is restricted; it must be in the month of Ramadan. Second, in the case of performing it in its proper time, expiation is obligatory by scholarly consensus. In the case of making it up, expiation is not obligatory for having intercourse. Third, if a person breaks his fast during the day without an excuse while performing it in its proper time, his fast is invalid, but he is required to abstain for the rest of the day, yes, out of respect for the time. As for making it up, if a person breaks his fast during the day, his fast is invalid, but he is not required to abstain, because there is no sanctity to the time in making it up, since making it up is broad and permissible on all days.
Source
ابن العثيمين - فتاوى الصيام — archive.org (30:03)
The Arabic text is a machine transcription of the audio recording.