I said to 'Umar bin al Khattab ؓ , ʿAnd when you (Muslims) travel in the land, there is no sin on you if you shorten As­Salah (the prayer) if you fear that the disbelievers may put you in trial (attack you)ʿ (al Nisa' 4:101]. But now the people are safe. He said: I wondered the same thing as you are wondering, and I asked the Messenger of Allah ﷺ about that. He said: “It is a charity that Allah has bestowed upon you, so accept His charity.ʿ (Using translation from Aḥmad 174)   

أَنْ تَقْصُرُوا} [النساء 101] مِنَ الصَّلَاةِ إِنْ خِفْتُمْ وَقَدْ أَمِنَ النَّاسُ فَقَالَ عُمَرُ عَجِبْتُ مِمَّا عَجِبْتَ مِنْهُ فَسَأَلْتُ رَسُولَ اللهِ ﷺ عَنْ ذَلِكَ فَقَالَ «صَدَقَةٌ تَصَدَّقَ اللهُ بِهَا عَلَيْكُمْ فَاقْبَلُوا صَدَقَتَهُ»  

He said to 'Abdullah bin 'Umar: "We find (mention of) prayer when one is at home (i.e., not traveling) and prayer at times of fear in the Qur'an, but we do not find any mention in the Qur'an of prayer when traveling. Ibn Umar said to him: 'O son of my brother, Allah (SWT) send Muhammad ﷺ to us when we did not know anything, and all we should do is to do that which we saw Muhammad ﷺ doing.'" (Using translation from Nasāʾī 1434)  

لَهُ ابْنُ عُمَرَ «ابْنَ أَخِي إِنَّ اللهَ بَعَثَ إِلَيْنَا مُحَمَّدًا ﷺ وَلَا نَعْلَمُ شَيْئًا فَإِنَّمَا نَفْعَلُ كَمَا رَأَيْنَا مُحَمَّدًا ﷺ يَفْعَلُ»  

The Messenger of Allah ﷺ set out from Makkah to Al-Madinah, fearing nothing but the Lord of the worlds, and praying two rak'ahs. (Using translation from Nasāʾī 1435)  

أَنَّ رَسُولَ اللهِ ﷺ «خَرَجَ مِنْ مَكَّةَ إِلَى الْمَدِينَةِ لَا يَخَافُ إِلَّا رَبَّ الْعَالَمِينَ فَصَلَّى رَكْعَتَيْنِ»  

"We used to travel with the Messenger of Allah ﷺ between Makkah and Al-Madinah, fearing nothing but Allah, the Mighty and Sublime, and praying two rak'ahs." (Using translation from Nasāʾī 1436)  

«كُنَّا نَسِيرُ مَعَ النَّبِيِّ ﷺ بَيْنَ مَكَّةَ وَالْمَدِينَةِ لَا نَخَافُ إِلَّا اللهَ نُصَلِّي رَكْعَتَيْنِ»  

"I saw 'Umar bin Al-Khattab praying two rak'ahs in Dhul-Hulaifah and I asked him about that. He said: 'I am simply doing that which I saw the Messenger of Allah ﷺ doing.'" (Using translation from Nasāʾī 1437)  

«إِنَّمَا أَفْعَلُ كَمَا رَأَيْتُ رَسُولَ اللهِ ﷺ يَفْعَلُ»  

"I went out with the Messenger of Allah ﷺ from Al-Madinah to Mekkah, and he continued to shorten his prayers, and he stayed there for ten days." (Using translation from Nasāʾī 1438)  

خَرَجْتُ مَعَ النَّبِيِّ ﷺ «مِنَ الْمَدِينَةِ إِلَى مَكَّةَ فَلَمْ يَزَلْ يَقْصُرُ حَتَّى رَجَعَ وَأَقَامَ بِهَا عَشْرًا»  

"I prayed two rak'ahs with the Messenger of Allah ﷺ on a journey, and two rak'ahs with Abu Bakr, and two rak'ahs with 'Umar, may Allah (SWT) be pleased with them both." (Using translation from Nasāʾī 1439)  

«صَلَّيْتُ مَعَ رَسُولِ اللهِ ﷺ فِي السَّفَرِ رَكْعَتَيْنِ وَمَعَ أَبِي بَكْرٍ رَكْعَتَيْنِ وَمَعَ عُمَرَ رَكْعَتَيْنِ»  

"The prayer for jumu'ah is two rak'ahs, and for Al-Fitr is two rak'ahs, and for An-Nahr is two rak'ahs, and for traveling is two rak'ahs, complete and not shortened, on the tongue of the Prophet ﷺ." (Using translation from Nasāʾī 1440)  

«صَلَاةُ الْجُمُعَةِ رَكْعَتَانِ وَالْفِطْرِ رَكْعَتَانِ وَالنَّحْرِ وَالسَّفَرِ رَكْعَتَانِ تَمَامٌ غَيْرُ قَصْرٍ عَلَى لِسَانِ النَّبِيِّ ﷺ»  

"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»  

Allah has prescribed the prayer through the word of your Prophet ﷺ as four rak'ahs when resident, two when travelling, and one when danger is present. (Using translation from Muslim 687a)  

«إِنَّ اللهَ فَرَضَ الصَّلَاةَ عَلَى لِسَانِ نَبِيِّكُمْ ﷺ فِي الْحَضَرِ أَرْبَعًا وَفِي السَّفَرِ رَكْعَتَيْنِ وَفِي الْخَوْفِ رَكْعَةً»