Sahih al-Bukhari 1089
Sahih al-Bukhari · Book 18: Shortening the Prayers (At-Taqseer) · When a traveller leaves his original place, he can shorten his Salat (prayer)
Narrated Anas bin Malik:
حَدَّثَنَا أَبُو نُعَيْمٍ ، قَالَ حَدَّثَنَا سُفْيَانُ ، عَنْ مُحَمَّدِ بْنِ الْمُنْكَدِرِ ، وَإِبْرَاهِيمَ بْنِ مَيْسَرَةَ ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ صَلَّيْتُ الظُّهْرَ مَعَ النَّبِيِّ صلى الله عليه وسلم بِالْمَدِينَةِ أَرْبَعًا، وَبِذِي الْحُلَيْفَةِ رَكْعَتَيْنِ.
offered four rak`at of Zuhr prayer with the Prophet (p.b.u.h) at Medina and two rak`at at Dhul-Hulaifa. (i.e. shortened the `Asr prayer).