I asked, or someone asked, the Messenger of Allah ﷺ 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. If you do that, you will have fasted perpetually and broken your fast as well."
حدثنا الحسين بن محمد الجريري ومحمد بن مدويه قالا حدثنا عبيد الله بن موسى أخبرنا هارون بن سلمان
سألت أو سئل رسول الله ﷺ عن صيام الدهر فقال إن لأهلك عليك حقا صم رمضان والذي يليه وكل أربعاء وخميس فإذا أنت قد صمت الدهر وأفطرت
[Its chain of transmission is daif] Abu Dawud narrated it in the Book of Fasting, Chapter on Fasting in Shawwal, hadith no. 2432, from the hadith of Ubaydullah bin Musa, through this same route. Ubaydullah al-Qurashi is unknown to me in terms of being criticized or endorsed, and the rest of the chain is strong.There is also a version on this subject narrated from Ayesha [mentioned previously, no. 746].