Sunan an-Nasa'i, Volume 3, Book 22, Hadith 2345 (DarusSalam) ⓘ
It was narrated from Ibn 'Umar that he used to say: "None should fast except the one who intended to fast before dawn."
قَالَ الْحَارِثُ بْنُ مِسْكِينٍ قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، عَنِ ابْنِ الْقَاسِمِ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّهُ كَانَ يَقُولُ لاَ يَصُومُ إِلاَّ مَنْ أَجْمَعَ الصِّيَامَ قَبْلَ الْفَجْرِ .
also referenced under: Hadith 2343 (Reference) & Book 22, Hadith 254 (In-Book)