Sahih al-Bukhari 1111

Arabic

حَدَّثَنَا حَسَّانُ الْوَاسِطِيُّ، قَالَ حَدَّثَنَا الْمُفَضَّلُ بْنُ فَضَالَةَ، عَنْ عُقَيْلٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَنَسِ بْنِ مَالِكٍ ـ رضى الله عنه ـ قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا ارْتَحَلَ قَبْلَ أَنْ تَزِيغَ الشَّمْسُ أَخَّرَ الظُّهْرَ إِلَى وَقْتِ الْعَصْرِ، ثُمَّ يَجْمَعُ بَيْنَهُمَا، وَإِذَا زَاغَتْ صَلَّى الظُّهْرَ ثُمَّ رَكِبَ‏.‏

English translation

Narrated Anas bin Malik:Whenever the Prophet (ﷺ) started the journey before noon, he used to delay the Zuhr prayer till the time for the `Asr prayer and then he would dismount and pray them together; and whenever the sun declined before he started the journey he used to offer the Zuhr prayer and then ride (for the journey)

Reference: Sahih al-Bukhari 1111, Book of Shortening the Prayers (At-Taqseer). English translation by Dr. Muhammad Muhsin Khan.