Sahih Muslim Book 6, Hadith Number 2582.

Chapter : The fasts observed by the Apostle of Allah (may peace be upon him) besides Ramadhan.

‘Aisha (Allah be pleased with her) reported: The Messenger of Allah (may peace be upon him) did not observe fast in any month of the year more than in the month of Sha’ban, and used to say: Do as many deeds as you are capable of doing, for Allah will not become weary (of giving you reward), but you would be tired (of doing good deeds); and he also said: The deed liked most by Allah is one to which the doer adheres constantly even if it is small.