The iqamah for the morning prayer was pronounced and the Messenger of Allah ﷺ began to offer prayer while he was looking at the mountain-pass. (AbuDawud elaborated that the Prophet had sent a horseman to the mountain-pass at night in order to keep watch.)  

ثُوِّبَ بِالصَّلاَةِ يَعْنِي صَلاَةَ الصُّبْحِ فَجَعَلَ رَسُولُ اللَّهِ ﷺ يُصَلِّي وَهُوَ يَلْتَفِتُ إِلَى الشِّعْبِ