The Book of Fasting
13/26. Chapter:
It is Permissible to delay making up missed Ramadan Fasts until before the next Ramadan comes, and this is for those who broke the fast for a reason such as sickness, travel, menstruation and the like
Sahih Muslim
حَدَّثَنَا أَحْمَدُ بْنُ عَبْدِ اللَّهِ بْنِ يُونُسَ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ أَبِي، سَلَمَةَ قَالَ سَمِعْتُ عَائِشَةَ، - رضى الله عنها - تَقُولُ كَانَ يَكُونُ عَلَىَّ الصَّوْمُ مِنْ رَمَضَانَ فَمَا أَسْتَطِيعُ أَنْ أَقْضِيَهُ إِلاَّ فِي شَعْبَانَ الشُّغُلُ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَوْ بِرَسُولِ اللَّهِ صلى الله عليه وسلم .
Abu Salama reported: I heard 'A'isha (Allah be pleased with her) as saying: I had to complete some of the fasts of Ramadan, but I could not do it but during the month of Sha'ban due to my duties to the Messenger of Allah (ﷺ) or with the Messenger of Allah (ﷺ).
Reference : Sahih Muslim 1146aIn-book reference : Book 13, Hadith 193USC-MSA web (English) reference : Book 6, Hadith 2549