The prayer was prescribed as consisting of two rak'ahs both when one was resident and when travelling. The prayer while travelling was left according to the original prescription and the prayer of one who was resident was enhanced.  

فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ رَكْعَتَيْنِ فِي الْحَضَرِ وَالسَّفَرِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَزِيدَ فِي صَلاَةِ الْحَضَرِ  

I remarked to 'Umar al-Khattab: Have you seen the shortening of the prayer by the people today while Allah has said: "If you fear that those who are infidels may afflict you", whereas those days are gone now? He replied: I have wondered about the same matter for which you wondered. So I mentioned this to the Messenger of Allah ﷺ. He said: It is an act of charity which Allah has done to you, so accept his charity.  

أَنْ يَفْتِنَكُمُ الَّذِينَ كَفَرُوا } فَقَدْ ذَهَبَ ذَلِكَ الْيَوْمُ فَقَالَ عَجِبْتُ مِمَّا عَجِبْتَ مِنْهُ فَذَكَرْتُ ذَلِكَ لِرَسُولِ اللَّهِ ﷺ فَقَالَ صَدَقَةٌ تَصَدَّقَ اللَّهُ بِهَا عَلَيْكُمْ فَاقْبَلُوا صَدَقَتَهُ  

This has been transmitted by Abu 'Asim and Hammad b. Mas'adah as transmitted by Ibn Bakr.