Sunan an-Nasa'i 3832
سنن النسائي#3832Sahihأَخْبَرَنَا أَحْمَدُ بْنُ يَحْيَى بْنِ الْوَزِيرِ بْنِ سُلَيْمَانَ، وَالْحَارِثُ بْنُ مِسْكِينٍ، قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، عَنِ ابْنِ وَهْبٍ، قَالَ أَخْبَرَنِي عَمْرُو بْنُ الْحَارِثِ، عَنْ كَعْبِ بْنِ عَلْقَمَةَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ شِمَاسَةَ، عَنْ عُقْبَةَ بْنِ عَامِرٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " كَفَّارَةُ النَّذْرِ كَفَّارَةُ الْيَمِينِ " .
It was narrated from 'Uqbah bin 'Amir that the Messenger of Allah said:"The expiation for vows is the expiation for an oath
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: 35:72