حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ رَافِعٍ، عَنْ خَالِدِ بْنِ يَزِيدَ، عَنْ عُقْبَةَ بْنِ عَامِرٍ الْجُهَنِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ مَنْ نَذَرَ نَذْرًا وَلَمْ يُسَمِّهِ فَكَفَّارَتُهُ كَفَّارَةُ يَمِينٍ ‏"‏ ‏.‏

It was narrated from 'Uqbah bin 'Amit Al-Juhani that the Messenger of Allah (PBUH) said: "Whoever makes a vow and does not state it specifically, the expiation (for such a vow) is the expiation for breaking an oath. " Translation Not Available

Book Ref: Sunan Ibn Majah Book 11 Hadith 2127
Web Ref:  Sunan Ibn Majah Vol 3 Book 11 Hadith 2127