I asked, or the Prophet ﷺ was asked, about fasting perpetually. He said, "Your family has a right over you. Fast Ramadan and the month that follows it, and every Wednesday and Thursday, and you will have fasted perpetually."
حدثنا محمد بن عثمان العجلي حدثنا عبيد الله يعني ابن موسى عن هارون بن سلمان
سألت أو سئل النبي ﷺ عن صيام الدهر فقال إن لأهلك عليك حقا صم رمضان والذي يليه وكل أربعاء وخميس فإذا أنت قد صمت الدهر
[Its chain of transmission is daif] Tirmidhi transmitted it in the chapter on fasting Wednesday and Thursday, no. 748, from the hadith of Ubaydullah bin Musa through this route, and he said, "Gharib." Ubaydullah bin Muslim, I did not find him.