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  

The prayer was prescribed as two rak'ahs, two rak'ahs both in journey and at the place of residence. The prayer while travelling remained as it was (originally prescribed), but an addition was made in the prayer (observed) at the place of residence.  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ رَكْعَتَيْنِ فِي الْحَضَرِ وَالسَّفَرِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَزِيدَ فِي صَلاَةِ الْحَضَرِ  

"The prayer of the resident was enjoined on the tongue of your Prophet ﷺ, four (rak'ahs), and the prayer of the traveler is two rak'ahs, and the prayer of fear is one rak'ah."  

فُرِضَتْ صَلاَةُ الْحَضَرِ عَلَى لِسَانِ نَبِيِّكُمْ ﷺ أَرْبَعًا وَصَلاَةُ السَّفَرِ رَكْعَتَيْنِ وَصَلاَةُ الْخَوْفِ رَكْعَةً  

"The first time the Salah was enjoined it was two Rak'ahs, and it remained as such when traveling, but the Salah while resident was made complete."  

أَوَّلَ مَا فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَأُتِمَّتْ صَلاَةُ الْحَضَرِ  

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  

Yahya related to me from Malik from Salih ibn Kaysan from Urwa ibn az-Zubayr that A'isha, the wife of the Prophet ﷺ said, "The prayer was prescribed as two rakas, both when settled and when travelling. Then the travelling prayer was kept as it was, and an increase was made in the prayer when settled. "  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ رَكْعَتَيْنِ فِي الْحَضَرِ وَالسَّفَرِ فَأُقِرَّتْ صَلاَةُ السَّفَرِ وَزِيدَ فِي صَلاَةِ الْحَضَرِ  

[Machine] The prayer was prescribed as two units, but the Messenger of Allah ﷺ added in the prayer of noon and left the prayer of travel as it is.  

فُرِضَتِ الصَّلَاةُ رَكْعَتَيْنِ فَزَادَ رَسُولُ اللهِ ﷺ فِي صَلَاةِ الْحَضَرِ وَتَرَكَ صَلَاةَ السَّفَرِ عَلَى نَحْوِهَا  

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. (Using translation from Abū Dāʾūd 1198)  

أَنَّهَا قَالَتْ «فُرِضَتِ الصَّلَاةُ رَكْعَتَيْنِ رَكْعَتَيْنِ فِي الْحَضَرِ وَالسَّفَرِ فَأُقِرَّتْ صَلَاةُ السَّفَرِ وَزِيدَ فِي الْحَضَرِ»  

[Machine] I heard Al-Sa'ib bin Yazid Al-Kindi, the son of the daughter of Al-Namir, saying, "Prayer was initially prescribed as two units of prayer, then it was increased during the Salah of Al-Hadar (residing) and the prayer of Al-Safar (travel) was made shorter."  

سَمِعْتُ السَّائِبَ بْنَ يَزِيدَ الْكِنْدِيَّ ابْنَ أُخْتِ النَّمِرِ يَقُولُ «فُرِضَتِ الصَّلَاةُ رَكْعَتَيْنِ رَكْعَتَيْنِ ثُمَّ زِيدَ فِي صَلَاةِ الْحَضَرِ وَأُقِرَّتْ صَلَاةُ السَّفَرِ»  

"The Salah was enjoined two Rak'ahs at a time, then the Salah when traveling remained like that, but the Salah while resident was increased." (Using translation from Nasāʾī 455)  

«فُرِضَتِ الصَّلَاةُ رَكْعَتَيْنِ فَأُقِرَّتْ صَلَاةُ السَّفَرِ وَزِيدَ فِي صَلَاةِ الْحَضَرِ»  

"The prayer of the resident was enjoined on the tongue of your Prophet ﷺ, four (rak'ahs), and the prayer of the traveler is two rak'ahs, and the prayer of fear is one rak'ah." (Using translation from Nasāʾī 1441)  

«فُرِضَتْ صَلَاةُ الْحَضَرِ عَلَى لِسَانِ نَبِيِّكُمْ أَرْبَعًا وَصَلَاةُ السَّفَرِ رَكْعَتَيْنِ وَصَلَاةُ الْخَوْفِ رَكْعَةً»  

"The prayer of the resident was enjoined on the tongue of your Prophet ﷺ, four (rak'ahs), and the prayer of the traveler is two rak'ahs, and the prayer of fear is one rak'ah." (Using translation from Nasāʾī 1441)  

«فُرِضَتْ صَلَاةُ الْحَضَرِ عَلَى لِسَانِ نَبِيِّكُمْ ﷺ أَرْبَعًا وَصَلَاةُ السَّفَرِ رَكْعَتَيْنِ وَصَلَاةُ الْخَوْفِ رَكْعَةً»