Sunan an-Nasa'i 2380
سنن النسائي#2380SahihIt was narrated from Mutarrif bin 'Abdullah bin 'Abdullah bin Ash-Shikhkhir:"My father told me that he heard the Messenger of Allah say, when mention was made in his presence of a man 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 ZaiSahih
In-book reference: 22:291