Mishkat al-Masabih 1338
Hafs b. ‘Asim said:
I accompanied Ibn ‘Umar on the road to Mecca and he led us in two rak'as at the noon prayer, then went to the place where he had alighted and sat down. Seeing some people standing he asked what they were doing, and I replied that they were engaged in glorifying God. He said, “If I had done so I would have perfected my prayer. I accompanied God's Messenger, and he prayed two rak'as and nothing more while on a journey. I also accompanied Abu Bakr, ‘Umar and ‘Uthman, and they did the same." 

(Bukhari and Muslim.)
وَعَنْ حَفْصِ بْنِ عَاصِمٍ قَالَ: صَحِبْتُ ابْنَ عُمَرَ فِي طَرِيقِ مَكَّةَ فَصَلَّى لَنَا الظُّهْرَ رَكْعَتَيْنِ ثُمَّ جَاءَ رَحْلَهُ وَجَلَسَ فَرَأَى نَاسًا قِيَامًا فَقَالَ: مَا يَصْنَعُ هَؤُلَاءِ؟ قُلْتُ: يُسَبِّحُونَ. قَالَ: لَوْ كُنْتُ مُسَبِّحًا أَتْمَمْتُ صَلَاتِي. صَحِبْتُ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَكَانَ لَا يَزِيدُ فِي السَّفَرِ عَلَى رَكْعَتَيْنِ وَأَبَا بكر وَعمر وَعُثْمَان كَذَلِك