Fasting is one of the most beloved worship in the sight of Allah. In this concern, it is narrated by Al-Bukhari on the authority of Abu Hurairah (May Allah be pleased with him) who reported: The Messenger of Allah (ﷺ) said, "Allah the Exalted and Majestic said: (The Fast is for Me and I will give the reward for it, as he (the one who observes the fast) leaves his sexual desire, food and drink for My Sake.)
Accordingly, it was the sunnah of Prophet Muhammad to make voluntary fasting at different days throughout the year other than the month of Ramadan.

Also, it was His sunnah to fast more days at some months than others. Month of Sha`ban was the month where the Prophet fasted more than other months except Ramadan. In this concern, Narrated Ummul-Mu'mineen `Aisha, Radi-Allahu anha,: (Allah's Messenger (ﷺ) used to fast till one would say that he would never stop fasting, and he would abandon fasting till one would say that he would never fast. I never saw Allah's Messenger (ﷺ) fasting for a whole month except the month of Ramadan, and did not see him fasting in any month more than in the month of Sha'ban.)
Ummul-Mu'mineen Umm Salamah, Radi-Allahu anha, says: "I have never seen the Messenger of Allah fasting for two months continuously except in the months of Sha'ban and Ramadan."
Prophet Muhammad fasted most of Sha`aban which made Umm Salamah, Radi-Allahu anha, said that he used to fast all Sha`ban, or it may be that their fasting at sha`ban coincided which made her believe that the Prophet fasted the entire of sha`ban.
It is a fact that the Prophet never fasted any enire month except Ramadan which is demonstrated in the narration related by Al-Bukhari on the authority of Aishah,: (I never saw the Messenger of Allah, Sall-Allahu alayhi wa sallam, fasting a complete month, except the month of Ramadan….)
Let’s fast many days at the month of sha`ban following the steps of the Prophet and to prepare our bosies and souls for the month of Ramadan.

http://300035.dotdothktrade.tech/en/artical/3407695/326-sunnah-fasting-most-sha`ban