Sunan an-Nasa'i, Volume 3, Book 22, Hadith 2188 (DarusSalam) ⓘ
It was narrated from Jubair bin Nufair that a man asked Aishah about fasting and she said: "The Messenger of Allah used to fast all of Shaban, and he made sure to fast on Mondays and Thursdays." '
أَخْبَرَنِي عَمْرُو بْنُ عُثْمَانَ، عَنْ بَقِيَّةَ، قَالَ حَدَّثَنَا بَحِيرٌ، عَنْ خَالِدٍ، عَنْ جُبَيْرِ بْنِ نُفَيْرٍ، أَنَّ رَجُلاً، سَأَلَ عَائِشَةَ عَنِ الصِّيَامِ، فَقَالَتْ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَصُومُ شَعْبَانَ كُلَّهُ وَيَتَحَرَّى صِيَامَ الاِثْنَيْنِ وَالْخَمِيسِ .
also referenced under: Hadith 2186 (Reference) & Book 22, Hadith 97 (In-Book)