(22) The Book of Fasting
كتاب الصيام
(68) Chapter: Mentioning the Differences Narrated by those who Reported the Narration from Hafsah concerning that
(68) باب ذِكْرِ اخْتِلاَفِ النَّاقِلِينَ لِخَبَرِ حَفْصَةَ فِي ذَلِكَ
Sunan an-Nasa'i 2342 
It was narrated that Ibn 'Umar said:
"If a man does not intend to fast from the night before, he should not fast."
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا الْمُعْتَمِرُ، قَالَ سَمِعْتُ عُبَيْدَ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ إِذَا لَمْ يُجْمِعِ الرَّجُلُ الصَّوْمَ مِنَ اللَّيْلِ فَلاَ يَصُمْ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 2342
In-book reference : Book 22, Hadith 253
English translation : Vol. 3, Book 22, Hadith 2344