Sunan an-Nasa'i, Book 22, Hadith 251 (In-Book) ⓘ
It was narrated that Hafsah said: "There is no fast for the one who does not intend to fast before dawn." Malik bin Anas narrated it in Mursla from.
أَخْبَرَنَا أَحْمَدُ بْنُ حَرْبٍ، حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ حَمْزَةَ بْنِ عَبْدِ اللَّهِ، عَنْ حَفْصَةَ، قَالَتْ لاَ صِيَامَ لِمَنْ لَمْ يُجْمِعِ الصِّيَامَ قَبْلَ الْفَجْرِ . أَرْسَلَهُ مَالِكُ بْنُ أَنَسٍ .
also referenced under: Hadith 2340 (Reference) & Volume 3, Book 22, Hadith 2342 (DarusSalam)