"How can the Salah be shortened as Allah says: There is no sin on you if you shorten As-Salah (the prayer) if you are in fear?" [1] Ibn 'Umar said: "O son of my brother! The Messenger of Allah ﷺ came to us when we had gone astray and he taught us. One of the things that he taught us was that Allah, the Mighty and Sublime, has commanded us to pray two Rak'ahs when traveling." [1] An-Nisa' 4:101.  

أَنَّهُ قَالَ لاِبْنِ عُمَرَ كَيْفَ تَقْصُرُ الصَّلاَةَ وَإِنَّمَا قَالَ اللَّهُ ﷻ { فَلَيْسَ عَلَيْكُمْ جُنَاحٌ أَنْ تَقْصُرُوا مِنَ الصَّلاَةِ إِنْ خِفْتُمْ } فَقَالَ ابْنُ عُمَرَ يَا ابْنَ أَخِي إِنَّ رَسُولَ اللَّهِ ﷺ أَتَانَا وَنَحْنُ ضُلاَّلٌ فَعَلَّمَنَا فَكَانَ فِيمَا عَلَّمَنَا أَنَّ اللَّهَ ﷻ أَمَرَنَا أَنْ نُصَلِّيَ رَكْعَتَيْنِ فِي السَّفَرِ قَالَ الشُّعَيْثِيُّ وَكَانَ الزُّهْرِيُّ يُحَدِّثُ بِهَذَا الْحَدِيثِ عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ