Jami` at-Tirmidhi 706
جامع الترمذي#706Sahihحَدَّثَنَا هَنَّادٌ، وَيُوسُفُ بْنُ عِيسَى، قَالاَ حَدَّثَنَا وَكِيعٌ، عَنْ أَبِي هِلاَلٍ، عَنْ سَوَادَةَ بْنِ حَنْظَلَةَ، هُوَ الْقُشَيْرِيُّ عَنْ سَمُرَةَ بْنِ جُنْدَبٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَمْنَعَنَّكُمْ مِنْ سُحُورِكُمْ أَذَانُ بِلاَلٍ وَلاَ الْفَجْرُ الْمُسْتَطِيلُ وَلَكِنِ الْفَجْرُ الْمُسْتَطِيرُ فِي الأُفُقِ " . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ .
Samurah bin Jundub narrated that :the Messenger of Allah said: "Do not let the Adhan of Bilal prevent you from your Sahar, nor the drawn out Fajr, but the Fajr that spreads on the horizon
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 8:25