Sahih al-Bukhari 1102
Sahih al-Bukhari · Book 18: Shortening the Prayers (At-Taqseer) · Whoever did not offer the Nawafil before and after the (compulsory) Salat during a journey
Narrated Ibn `Umar:
حَدَّثَنَا مُسَدَّدٌ ، قَالَ حَدَّثَنَا يَحْيَى ، عَنْ عِيسَى بْنِ حَفْصِ بْنِ عَاصِمٍ ، قَالَ حَدَّثَنِي أَبِي أَنَّهُ، سَمِعَ ابْنَ عُمَرَ ، يَقُولُ صَحِبْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَكَانَ لاَ يَزِيدُ فِي السَّفَرِ عَلَى رَكْعَتَيْنِ ، وَأَبَا بَكْرٍ وَعُمَرَ وَعُثْمَانَ كَذَلِكَ ـ رضى الله عنهم .
I accompanied Allah's Messenger (ﷺ) and he never offered more than two rak`at during the journey. Abu Bakr, `Umar and `Uthman used to do the same.