عَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا أَنَّهَا سُئِلَتْ عَنْ صَوْمِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَتْ: كَانَ يَصُومُ شَعْبَانَ وَيَتَحَرَّى الْإِثْنَيْنِ وَالْخَمِيسَ
When Lady Aisha (may Allah be pleased with her) was asked about the fasts of the Messenger of Allah (peace and blessings be upon him), she said: He (peace and blessings be upon him) used to fast in the month of Sha'ban and would especially observe fasts on Mondays and Thursdays.