كان يصوم شعبان إلا قليلا

 The collection of An-Nawawi Forty (40) Hadith Pocket Size (Paperback)

رياض الصالحين بالعربية والإنجليزية - (ج 1 / ص 1597)
1247 - وعن عائشة رضي الله عنها قالت : لم يكن النبي صلى الله عليه و سلم يصوم من شهر أكثر من شعبان فإنه كان يصوم شعبان كله
وفي رواية : كان يصوم شعبان إلا قليلا . متفق عليه

 `Aishah (May Allah be pleased with her) reported: The Prophet (PBUH) did not observe voluntary Saum (fasting) so frequently during any other month as he did during Sha`ban. He observed Saum throughout the month of Sha`ban.

Another narration is: He (PBUH) observed Saum during the whole month of Sha`ban except a few days.
[Al-Bukhari and Muslim].

Commentary:

We learn from another Hadith the reason why the Prophet (PBUH) kept greater number of Saum in the month of Sha`ban. He did so because deeds are presented before Allah during this month. For this reason, he liked that when his deeds were presented, he should be observing Saum (Nasa'i on the authority of Usamah (May Allah be pleased with him). In spite of this distinction of Sha`ban, Muslims have been ordered to observe Saum in the first fortnight only, and not in the second in order to maintain their energy and vitality for the obligatory Saum (i.e., Ramadan). The Prophet (PBUH) had greater spiritual strength and Saum did not cause him weakness due to this strength. Again, by virtue of this strength he would sometimes even observe Saum which is termed "Saum-al-Wisal'' (observing Saum continuous without a break in the evening). But he has forbidden his followers from such Saum.