The Messenger of Allah ﷺ said about fasting perpetually, "He has neither fasted nor broken his fast."
أخبرنا محمد بن المثنى قال حدثنا أبو داود قال حدثنا شعبة عن قتادة قال سمعت
أن رسول الله ﷺ قال في صوم الدهر لا صام ولا أفطر
[Its chain of transmission is sahih] Ibn Majah narrated it, no. 1705, from the hadith of Abu Dawud Tayalisi through this route (see the previous hadith), and it is in Kubra, no. 2684, and Musnad Tayalisi, no. 1147. Ibn Khuzayma graded it sahih, no. 2150, and so did Ibn Hibban, no. 938.