Hadith 503340
Chapter 9: Shortening the Prayer - كتاب قصر الصلاة فى السفر
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، أَنَّهُ سَأَلَ سَالِمَ بْنَ عَبْدِ اللَّهِ هَلْ يُجْمَعُ بَيْنَ الظُّهْرِ وَالْعَصْرِ فِي السَّفَرِ فَقَالَ نَعَمْ لاَ بَأْسَ بِذَلِكَ أَلَمْ تَرَ إِلَى صَلاَةِ النَّاسِ بِعَرَفَةَ
Yahya related to me from Malik from Ibn Shihab that he had asked Salim ibn Abdullah, "Can you join dhuhr and asr when travelling?" He said, "Yes, there is no harm in that. Haven't you seen the people pray on Arafa?"
Reference Muwatta Malik 503340
USC-MSA web (English) reference : Book 9, Hadith 6