Surah Al-Baqarah, verse 184

أَيَّامًا مَّعْدُودَٰتٍ ۚ فَمَن كَانَ مِنكُم مَّرِيضًا أَوْ عَلَىٰ سَفَرٍ فَعِدَّةٌ مِّنْ أَيَّامٍ أُخَرَ ۚ وَعَلَى ٱلَّذِينَ يُطِيقُونَهُۥ فِدْيَةٌ طَعَامُ مِسْكِينٍ ۖ فَمَن تَطَوَّعَ خَيْرًا فَهُوَ خَيْرٌ لَّهُۥ ۚ وَأَن تَصُومُوا۟ خَيْرٌ لَّكُمْ ۖ إِن كُنتُمْ تَعْلَمُونَ ﴿١٨٤﴾

2:184 [Fast is for] specific number of days; but if anyone of you is ill or on a journey, he should make up for those days. As for those who can only fast with hardship, a compensation can be made by feeding a needy person [for each day]. But anyone who volunteers to give more, it is better for him. Yet fasting is better for you, if only you knew