Sunan an-Nasa'i, Hadith 2187 ⓘ
It was narrated that 'Aishah said: "The Messenger of Allah used to fast Sha`ban and Ramadan, and he made sure to fast on Mondays and Thursday."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ دَاوُدَ، قَالَ حَدَّثَنَا ثَوْرٌ، عَنْ خَالِدِ بْنِ مَعْدَانَ، عَنْ رَبِيعَةَ الْجُرَشِيِّ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصُومُ شَعْبَانَ وَرَمَضَانَ وَيَتَحَرَّى الاِثْنَيْنِ وَالْخَمِيسَ .
also referenced under: Book 22, Hadith 98 (In-Book) & Volume 3, Book 22, Hadith 2189 (DarusSalam)