Bulugh al-Maram #1568
كتاب الأيمان والنذور
وَلِأَبِي دَاوُدَ: مِنْ حَدِيثِ اِبْنِ عَبَّاسٍ مَرْفُوعاً: «مِنْ نَذَرَ نَذْراً لَمْ يُسَمِّهِ, فَكَفَّارَتُهُ كَفَّارَةُ يَمِينٍ, وَمَنْ نَذَرَ نَذْراً فِي مَعْصِيَةٍ, فَكَفَّارَتُهُ كَفَّارَةُ يَمِينٍ, وَمَنْ نَذَرَ نَذْراً لَا يُطِيقُهُ, فَكَفَّارَتُهُ كَفَّارَةُ يَمِينٍ» وَإِسْنَادُهُ صَحِيحٌ; إِلَّا أَنَّ اَلْحُفَّاظَ رَجَّحُوا وَقْفَهُ.
Abu Dawud has from the narration of Ibn Abbas (RA) (who reported Allah's Messenger (ﷺ) as saying):
“If anyone takes a vow but does not name it, its atonement is the same as that for an oath. If anyone takes a vow to do an act of disobedience, its atonement is the same as that for an oath. If anyone takes a vow which he is unable to fulfill, its atonement is the same as that for an oath.”.