Narrated Sahl ibn al-Hanzaliyyah: 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 (ﷺ) had sent a horseman to the mountain-pass at night in order to keep watch.)
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا الرَّبِيعُ بْنُ نَافِعٍ، حَدَّثَنَا مُعَاوِيَةُ، - يَعْنِي ابْنَ سَلاَّمٍ - عَنْ زَيْدٍ، أَنَّهُ سَمِعَ أَبَا سَلاَّمٍ، قَالَ حَدَّثَنِي السَّلُولِيُّ، - هُوَ أَبُو كَبْشَةَ - عَنْ سَهْلِ ابْنِ الْحَنْظَلِيَّةِ، قَالَ ثُوِّبَ بِالصَّلاَةِ - يَعْنِي صَلاَةَ الصُّبْحِ - فَجَعَلَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي وَهُوَ يَلْتَفِتُ إِلَى الشِّعْبِ . قَالَ أَبُو دَاوُدَ وَكَانَ أَرْسَلَ فَارِسًا إِلَى الشِّعْبِ مِنَ اللَّيْلِ يَحْرُسُ .
sunnah.com