Addressing (the people) Samurah b. Jundub reported the Messenger of Allah (ﷺ) as saying:The adhan (call to prayer) of Bilal should not prevent you from taking a meal shortly before dawn, not does the whiteness of horizon (before dawn) in this way (vertically) until it spreads out horizontally.
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ عَبْدِ اللَّهِ بْنِ سَوَادَةَ الْقُشَيْرِيِّ، عَنْ أَبِيهِ، قَالَ سَمِعْتُ سَمُرَةَ بْنَ جُنْدُبٍ، يَخْطُبُ وَهُوَ يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَمْنَعَنَّ مِنْ سَحُورِكُمْ أَذَانُ بِلاَلٍ وَلاَ بَيَاضُ الأُفُقِ الَّذِي هَكَذَا حَتَّى يَسْتَطِيرَ " .
AbuDaud
Fasting (Kitab Al-Siyam) • Hadith 2346