(1) بَابُ مَا جَاءَ فِي إِجَازَةِ خَبَرِ الْوَاحِدِ الصَّدُوقِ فِي الأَذَانِ وَالصَّلاَةِ وَالصَّوْمِ وَالْفَرَائِضِ وَالأَحْكَامِ
Narrated Ibn Mas`ud:
Allah's Messenger (ﷺ) said, "The (call for prayer) Adhan of Bilal should not stop anyone of you from taking his Suhur for he pronounces the Adhan in order that whoever among you is praying the night prayer, may return (to eat his Suhur) and whoever among you is sleeping, may get up, for it is not yet dawn (when it is like this)." (Yahya, the sub-narrator stretched his two index fingers side ways).
Reference: Sahih al-Bukhari 7247
In-book reference: Book 95, Hadith 2
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 91, Hadith 353