The Holy Prophet (SallAllahu Alayhi wa Sallam) used to fast in Sha'ban abundantly

It is mentioned in Sahih Bukhari: Sayyidatuna Ayesha Siddiqah (Radi Allahu Anha) said that the Beloved Prophet (SallAllahu Alayhi wa Sallam) would not fast so abundantly in any other month as he (SallAllahu Alayhi wa Sallam) would in Sha'ban, rather he (SallAllahu Alayhi wa Sallam) used to fast the whole month and would say, "Act according to your capability as Allah does not cease His blessings until you become exhausted." [Sahih Bukhari, Vol. 1, Page 648, Hadith 1970]

Allamah Mufti Sharif al-Haq Amjadi (Alayhir Rahmah) has elaborated on this hadith as follows: It means that he used to observe fasts in most of the days of Sha'ban and it was referred to as the whole (i.e. the fasts of the whole month). It is usually said, "Such and such a person worshipped the whole night"; although he would have spent time in eating and answering his needs. In such cases, "mostly" is referred to as "the whole".

He (Alayhir Rahmah) further stated: From this hadith we learn that one bearing the capability to do so, should observe fasts extensively. However, the one who is weak should not fast as it may adversely affect his capability to fast in the month of Ramadan. The same point has been asserted in those Ahadith in which it was stated, "Do not fast after the first half of Sha'ban."
[Nuzhat al-Qari Sharh Sahih al-Bukhari, Vol. 3, Page 377-380]