Sunan an-Nasa'i 2368
سنن النسائي#2368Hasanأَخْبَرَنَا مُحَمَّدُ بْنُ عَلِيِّ بْنِ الْحَسَنِ بْنِ شَقِيقٍ، قَالَ أَبِي أَنْبَأَنَا أَبُو حَمْزَةَ، عَنْ عَاصِمٍ، عَنْ زِرٍّ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصُومُ ثَلاَثَةَ أَيَّامٍ مِنْ غُرَّةِ كُلِّ شَهْرٍ وَقَلَّمَا يُفْطِرُ يَوْمَ الْجُمُعَةِ .
It was narrated that 'Abdullah bin Masud said:"The Messenger of Allah used to fast three days in the middle of every month, and he rarely did not fast on Friday
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahHasan
Al-AlbaniHasan
Zubair Ali ZaiIsnaad Hasan
In-book reference: 22:279