The Messenger of Allah ﷺ used to fast to such an extent that we thought that he would never break his fast, and he would go without fasting to such an extent that we thought he would never fast. I never saw the Messenger of Allah ﷺ fast a complete month except in Ramadan, and I never saw his fast more in any month than in Sha'ban. (Using translation from Abū Dāʾūd 2434)
أَنَّهَا قَالَتْ كَانَ رَسُولُ اللهِ ﷺ يَصُومُ حَتَّى نَقُولَ لَا يُفْطِرُ وَيُفْطِرُ حَتَّى نَقُولَ لَا يَصُومُ وَمَا رَأَيْتُ رَسُولَ اللهِ ﷺ اسْتَكْمَلَ صِيَامَ شَهْرٍ قَطُّ إِلَّا رَمَضَانَ وَمَا رَأَيْتُهُ فِي شَهْرٍ قَطُّ أَكْثَرَ صِيَامًا مِنْهُ فِي شَعْبَانَ