the mother of believers: Allah enjoined the prayer when He enjoined it, it was two rakʿat only (in every prayer) both when in residence or on journey. Then the prayers offered on journey remained the same, but (the rakʿat of) the prayers for non-travelers were increased.  

فَرَضَ اللَّهُ الصَّلاَةَ حِينَ فَرَضَهَا رَكْعَتَيْنِ رَكْعَتَيْنِ فِي الْحَضَرِ وَالسَّفَرِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَزِيدَ فِي صَلاَةِ الْحَضَرِ  

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}  

offered four rakʿat of Zuhr prayer with the Prophet ﷺ at Medina and two rakʿat at Dhul-Hulaifa. (i.e. shortened the ʿAsr prayer).  

صَلَّيْتُ الظُّهْرَ مَعَ النَّبِيِّ ﷺ بِالْمَدِينَةِ أَرْبَعًا وَبِذِي الْحُلَيْفَةِ رَكْعَتَيْنِ  

I heard Anas saying, "We traveled with the Prophet ﷺ from Medina to Mecca and offered two rakʿat (for every prayer) till we returned to Medina." I said, "Did you stay for a while in Mecca?" He replied, "We stayed in Mecca for ten days."  

سَمِعْتُ أَنَسًا يَقُولُ خَرَجْنَا مَعَ النَّبِيِّ ﷺ مِنَ الْمَدِينَةِ إِلَى مَكَّةَ فَكَانَ يُصَلِّي رَكْعَتَيْنِ رَكْعَتَيْنِ حَتَّى رَجَعْنَا إِلَى الْمَدِينَةِ قُلْتُ أَقَمْتُمْ بِمَكَّةَ شَيْئًا قَالَ أَقَمْنَا بِهَا عَشْرًا