Abdul 'Aziz bin Muhammad al-Daruradi عبد العزيز بن محمد الدراوردي · Fasting (Kitab Al-Siyam)

She never saw the Prophet (ﷺ) fasting the whole month except Sha'ban which he combined with Ramadan.

I asked or someone asked the Prophet (ﷺ) about perpetual fasting. He replied: You have a duty to your family. Fast during Ramadan and the following month, and every Wednesday and Thursday. You will then have observed a perpetual fast.