Muwatta Imam Malik Book of Shortening the Prayer, Hadith 8

Yahya related to me from Malik from Ibn Shihab from a man of the family of Khalid ibn Asid that he said to Abdullah ibn Umar, "Abu Abd ar-Rahman, we find the fear prayer and the prayer when settled mentioned in the Qur'an, but we do not find any mention of the travelling prayer in it." Ibn Umar said, "Son of my brother! Allah the Mighty and Majestic sent us Muhammad ﷺ and we know nothing. We only do as we saw him doing."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ رَجُلٍ، مِنْ آلِ خَالِدِ بْنِ أَسِيدٍ أَنَّهُ سَأَلَ عَبْدَ اللَّهِ بْنَ عُمَرَ فَقَالَ يَا أَبَا عَبْدِ الرَّحْمَنِ إِنَّا نَجِدُ صَلاَةَ الْخَوْفِ وَصَلاَةَ الْحَضَرِ فِي الْقُرْآنِ وَلاَ نَجِدُ صَلاَةَ السَّفَرِ فَقَالَ ابْنُ عُمَرَ يَا ابْنَ أَخِي إِنَّ اللَّهَ عَزَّ وَجَلَّ بَعَثَ إِلَيْنَا مُحَمَّدًا ﷺ وَلاَ نَعْلَمُ شَيْئًا فَإِنَّمَا نَفْعَلُ كَمَا رَأَيْنَاهُ يَفْعَلُ .