The Book of Fasting
13/8. Chapter:
Clarifying that fasting begins at dawn, and a person may eat and other than that until dawn begins; And clarifying the dawn which has to do with the rulings concerning the beginning of fasting and the beginning of the time for the Subh Prayer, and other than that, which is the Second Dawn, which is called the True Dawn. The First Dawn, which is the False Dawn, has nothing to do with the rulings
Sahih Muslim
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ سَوَادَةَ، قَالَ سَمِعْتُ سَمُرَةَ، بْنَ جُنْدَبٍ - رضى الله عنه - وَهُوَ يَخْطُبُ يُحَدِّثُ عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ " لاَ يَغُرَّنَّكُمْ نِدَاءُ بِلاَلٍ وَلاَ هَذَا الْبَيَاضُ حَتَّى يَبْدُوَ الْفَجْرُ - أَوْ قَالَ - حَتَّى يَنْفَجِرَ الْفَجْرُ " .
Samura b. Jundub addressed and narrated from the Messenger of Allah (ﷺ) having said (these words): Neither the call of Bilal should mislead you nor this whiteness (of false dawn) till (the true) dawn appears (or he said) till the dawn breaks.
Reference : Sahih Muslim 1094dIn-book reference : Book 13, Hadith 53USC-MSA web (English) reference : Book 6, Hadith 2410