Messenger of Allah 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 Messenger of Allah 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.
كَانَ رَسُولُ اللَّهِ ﷺ يَصُومُ حَتَّى نَقُولَ لاَ يُفْطِرُ وَيُفْطِرُ حَتَّى نَقُولَ لاَ يَصُومُ فَمَا رَأَيْتُ رَسُولَ اللَّهِ ﷺ اسْتَكْمَلَ صِيَامَ شَهْرٍ إِلاَّ رَمَضَانَ وَمَا رَأَيْتُهُ أَكْثَرَ صِيَامًا مِنْهُ فِي شَعْبَانَ