Sahih al-Bukhari, Hadith 634 ⓘ
Narrated `Aun bin Abi Juhaifa: My father said, "I saw Bilal turning his face from side to side while pronouncing the Adhan for the prayer."
حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَوْنِ بْنِ أَبِي جُحَيْفَةَ، عَنْ أَبِيهِ، أَنَّهُ رَأَى بِلاَلاً يُؤَذِّنُ فَجَعَلْتُ أَتَتَبَّعُ فَاهُ هَا هُنَا وَهَا هُنَا بِالأَذَانِ.
also referenced under: Book 10, Hadith 31 (In-Book) & Volume 1, Book 11, Hadith 607 (USC-MSA)