"My father told me: 'I was with Ibn Umar on a journey, and he prayed Zuhr and 'Asr with two rak'ahs each, then he went and sat on his carpet. He saw some people offering voluntary prayers and said: What are these people doing? I said: They are offering voluntary prayers. He said: If I had wanted to pray before and after (the obligatory prayer) I would have offered it in full. I accompanied the Messenger of Allah ﷺ and he did not pray more than two rak'ahs when traveling, and Abu Bakr (did likewise) until he died, as did 'Umar and 'Uthman, may Allah (SWT) be pleased with them all."  

مَا يَصْنَعُ هَؤُلاَءِ قُلْتُ يُسَبِّحُونَ قَالَ لَوْ كُنْتُ مُصَلِّيًا قَبْلَهَا أَوْ بَعْدَهَا لأَتْمَمْتُهَا صَحِبْتُ رَسُولَ اللَّهِ ﷺ فَكَانَ لاَ يَزِيدُ فِي السَّفَرِ عَلَى الرَّكْعَتَيْنِ وَأَبَا بَكْرٍ حَتَّى قُبِضَ وَعُمَرَ وَعُثْمَانَ ؓ كَذَلِكَ  

[Machine] If I prayed before or after it, I would complete it. I accompanied the Prophet ﷺ until he passed away, and he would not exceed two Rak'ahs. Abu Bakr, until he passed away, would not exceed them either, and Umar and Uthman were the same.  

لَوْ كُنْتُ مُصَلِّيًا قَبْلَهَا أَوْ بَعْدَهَا لَأَتْمَمْتُهَا صَحِبْتُ النَّبِيَّ ﷺ حَتَّى قُبِضَ فَكَانَ لَا يَزِيدُ عَلَى رَكْعَتَيْنِ وَأَبَا بَكْرٍ حَتَّى قُبِضَ فَكَانَ لَا يَزِيدُ عَلَيْهِمَا وَعُمَرَ وَعُثْمَانَ كَذَلِكَ