Sahih al-Bukhari 634
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · Should the Mu'adh-dhin turn his mouth (face) and look from side to side during the Adhan?
Narrated `Aun bin Abi Juhaifa:
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.
My father said, "I saw Bilal turning his face from side to side while pronouncing the Adhan for the prayer."