'Aishah (May Allah be pleased with her) reported:
The Prophet ﷺ 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 ﷺ observed Saum during the whole month of Sha'ban except a few days.

[Al-Bukhari and Muslim].

وعن عائشة رضي الله عنها قالت لم يكن النبي ﷺ يصوم من شهر أكثر من شعبان فإنه كان يصوم شعبان كله وفي رواية: كان يصوم شعبان إلا قليلا. ((متفق عليه))