Sunan an-Nasa'i 1709
سنن النسائي#1709Sahihأَخْبَرَنَا أَحْمَدُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا حُسَيْنٌ، عَنْ زَائِدَةَ، عَنْ سُلَيْمَانَ، عَنْ عُمَارَةَ بْنِ عُمَيْرٍ، عَنْ يَحْيَى بْنِ الْجَزَّارِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي مِنَ اللَّيْلِ تِسْعًا فَلَمَّا أَسَنَّ وَثَقُلَ صَلَّى سَبْعًا .
It was narrated that 'Aishah said:"The Messenger of Allah (ﷺ) used to pray nine (rak'ahs) at night, then when he grew older and put on weight he prayed seven
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 GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 20:112