The Prophet ﷺ said, "Whoever fasts forever has neither fasted nor broken his fast."
حدثنا أبو بكر بن أبي شيبة حدثنا عبيد بن سعيد ح و حدثنا محمد بن بشار حدثنا يزيد بن هارون وأبو داود قالوا حدثنا شعبة عن قتادة
قال النبي ﷺ من صام الأبد فلا صام ولا أفطر
[Its chain is sahih] Nasai reported it, 4/207, Fasting, "The prohibition of fasting the entire year, and mention of the disagreement over Mutarrif bin Abdullah in the report on this," no. 2383, from the hadith of Abu Dawud Tayalisi through this route. Ibn Khuzayma graded it sahih, no. 2150, as did Ibn Hibban (Mawarid), no. 938, along with Hakim, 1/435, and Dhahabi.