Observing Fasts in Most of the Days of Shaban is Sunnah
The Mother of the believers, Sayyidatuna Aishah Siddiqah has reported: I never saw the Beloved and Blessed Prophet (May Peace and blessings of Allah be upon him) observing fasts so extensively in a month as in the month of Shaban. Leaving a few days, he used to fast the whole of the month.
(Sunan Tirmidhi, vol. 2, pp. 182, Hadis 736)