Sunan an-Nasa'i, Hadith 2319 ⓘ
It was narrated that 'Aishah said: "I would own fasts from Ramadan and I would not make them up until Shaban came."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، قَالَ سَمِعْتُ أَبَا سَلَمَةَ، يُحَدِّثُ عَنْ عَائِشَةَ، قَالَتْ إِنْ كَانَ لَيَكُونُ عَلَىَّ الصِّيَامُ مِنْ رَمَضَانَ فَمَا أَقْضِيهِ حَتَّى يَجِيءَ شَعْبَانُ .
also referenced under: Book 22, Hadith 230 (In-Book) & Volume 3, Book 22, Hadith 2321 (DarusSalam)