مُوَطَّأُ مَالِكٍ
Muwatta Malik 353
Shortening the Prayer
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ لَمْ يَكُنْ يُصَلِّي مَعَ صَلاَةِ الْفَرِيضَةِ فِي السَّفَرِ شَيْئًا قَبْلَهَا وَلاَ بَعْدَهَا إِلاَّ مِنْ جَوْفِ اللَّيْلِ فَإِنَّهُ كَانَ يُصَلِّي عَلَى الأَرْضِ وَعَلَى رَاحِلَتِهِ حَيْثُ تَوَجَّهَتْ .
Yahya related to me from Malik from Nafi that Abdullah ibn Umar never used to pray anything with the fard prayer, either before it or after it, while travelling, except in the depths of the night. He would pray on the ground or on his mount, whichever way it was facing.
Arabic/English book reference: Book 9, Hadith 24