Sunan an-Nasa'i 1311
سنن النسائي#1311Sahihأَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، عَنْ جَابِرٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَقُولُ فِي صَلاَتِهِ بَعْدَ التَّشَهُّدِ " أَحْسَنُ الْكَلاَمِ كَلاَمُ اللَّهِ وَأَحْسَنُ الْهَدْىِ هَدْىُ مُحَمَّدٍ صلى الله عليه وسلم " .
It was narrated from Jabir that:The Messenger of Allah (ﷺ) used to say in his prayer, after the tashahhud: "The best of word is the word of Allah (SWT) and the best of guidance is the guidance of Muhammad (ﷺ)
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:
In-book reference: 13:133