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.  

كَانَ يَكُونُ عَلَىَّ الصَّوْمُ مِنْ رَمَضَانَ فَمَا أَسْتَطِيعُ أَنْ أَقْضِيَهُ إِلاَّ فِي شَعْبَانَ الشُّغُلُ مِنْ رَسُولِ اللَّهِ ﷺ أَوْ بِرَسُولِ اللَّهِ ﷺ  

If I had some part of the fast of Ramadan to make up, I would not be able to atone for it except in Sha'ban.  

أَنَّهُ سَمِعَ عَائِشَةَ ؓ تَقُولُ إِنْ كَانَ لَيَكُونُ عَلَىَّ الصَّوْمُ مِنْ رَمَضَانَ فَمَا أَسْتَطِيعُ أَنْ أَقْضِيَهُ حَتَّى يَأْتِيَ شَعْبَانُ  

“I heard ‘Aishah say: ‘I used to owe fasts from the month of Ramadan, and I would not make them up for until Sha’ban came.’”  

سَمِعْتُ عَائِشَةَ تَقُولُ إِنْ كَانَ لَيَكُونُ عَلَىَّ الصِّيَامُ مِنْ شَهْرِ رَمَضَانَ فَمَا أَقْضِيهِ حَتَّى يَجِيءَ شَعْبَانُ  

"I would own fasts from Ramadan and I would not make them up until Shaban came." (Using translation from Nasāʾī 2319)  

«إِنْ كَانَ لَيَكُونُ عَلَيَّ الصِّيَامُ مِنْ رَمَضَانَ فَمَا أَقْضِيهِ حَتَّى يَجِيءَ شَعْبَانُ»