Ibn ʿUmar went on a journey and said, "I accompanied the Prophet ﷺ and he did not offer optional prayers during the journey, and Allah says: 'Verily! In Messenger of Allah ﷺ you have a good example to follow.' " (33.21)  

صَحِبْتُ النَّبِيَّ ﷺ فَلَمْ أَرَهُ يُسَبِّحُ فِي السَّفَرِ وَقَالَ اللَّهُ جَلَّ ذِكْرُهُ {لَقَدْ كَانَ لَكُمْ فِي رَسُولِ اللَّهِ أُسْوَةٌ حَسَنَةٌ}  

I accompanied Messenger of Allah ﷺ and he never offered more than two rakʿat during the journey. Abu Bakr, ʿUmar and ʿUthman used to do the same.  

أَنَّهُ سَمِعَ ابْنَ عُمَرَ يَقُولُ صَحِبْتُ رَسُولَ اللَّهِ ﷺ فَكَانَ لاَ يَزِيدُ فِي السَّفَرِ عَلَى رَكْعَتَيْنِ وَأَبَا بَكْرٍ وَعُمَرَ وَعُثْمَانَ كَذَلِكَ ؓ