كتاب الطلاق
Read the English translation first, with the original Arabic directly underneath.
Narrated 'Abdullah bin Mas'ud:
The Prophet (ﷺ) said, "The call (or the Adhan) of Bilal should not stop you from taking the Suhur-meals for Bilal calls (or pronounces the Adhan) so that the one who is offering the night prayer should take a rest, and he does not indicate the daybreak or dawn." The narrator, Yazid, described (how dawn breaks) by stretching out his hands and then separating them wide apart.
لاَ يَمْنَعَنَّ أَحَدًا مِنْكُمْ نِدَاءُ بِلاَلٍ ـ أَوْ قَالَ أَذَانُهُ ـ مِنْ سَحُورِهِ، فَإِنَّمَا يُنَادِي أَوْ قَالَ يُؤَذِّنُ لِيَرْجِعَ قَائِمُكُمْ