Sunan an-Nasa'i 2381
سنن النسائي#2381SahihMutarrif bin 'Abdullah bin Ash-Shikhkhir narrated from his father that:the Messenger of Allah said, concerning one who fasted for the rest of his life: "He neither fasted nor broke his fast." 'Ata said: "someone who heard him told me that Ibn 'Umar (said) that the Prophet said: 'Whoever fasts every day of his life, then he has not fasted
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 22:292