Sunan an-Nasa'i, Volume 2, Book 15, Hadith 1437 (DarusSalam) ⓘ
It was narrated that Ibn 'Abbas said: "We used to travel with the Messenger of Allah between Makkah and Al-Madinah, fearing nothing but Allah, the Mighty and Sublime, and praying two rak'ahs."
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا ابْنُ عَوْنٍ، عَنْ مُحَمَّدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ كُنَّا نَسِيرُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم بَيْنَ مَكَّةَ وَالْمَدِينَةِ لاَ نَخَافُ إِلاَّ اللَّهَ عَزَّ وَجَلَّ نُصَلِّي رَكْعَتَيْنِ .
also referenced under: Hadith 1436 (Reference) & Book 15, Hadith 4 (In-Book)