Surah Al Baqarah Verse 184 and the beginning of verse 185 explain that the fasting required of Muslims is several days, namely in the month of Ramadan according to the number of days of Ramadan, which is 29 or 30 days.
Surah Al Baqarah Verse 184 in Arabic, Transliteration, and English Translation
Ayyāmam ma’dụdāt, fa mang kāna mingkum marīḍan au ‘alā safarin fa ‘iddatum min ayyāmin ukhar, wa ‘alallażīna yuṭīqụnahụ fidyatun ṭa’āmu miskīn, fa man taṭawwa’a khairan fa huwa khairul lah, wa an taṣụmụ khairul lakum ing kuntum ta’lamụn
“(That is) a certain number of days. Then whoever among you is sick or on the way (and does not fast), then (is obliged to replace) as many days (which he did not fast) on other days. And for one who is strenuous in carrying it out, it is obligatory to pay fidyah, that is, to feed a poor man. But whoever by the willingness of heart works virtue, then it is better for him, and your fast is better for you if you know.” (Q.S Al Baqarah : 184)
The obligation to fast is a certain number of days in the month of Ramadan. So whoever among you is sick so that he is unable to fast, or on the way and does not fast, then he is obliged to change the fast as many days as he does not fast on other days. And for one who is strenuous in carrying it out because of a serious illness for which there is no hope of recovery or because it is very old, it is obligatory to pay fidyah or substitute i.e. feed a poor man for that one day who does not fast. But whoever by the willingness of heart works virtue and then feeds more than one poor man for one day not fasting, then it is better for him. And you all keep fasting, then the choice to keep fasting is better for you than giving fidyah, if you know the virtues of fasting according to God.