Sahih al-Bukhari 1112

Arabic

حَدَّثَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا الْمُفَضَّلُ بْنُ فَضَالَةَ، عَنْ عُقَيْلٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا ارْتَحَلَ قَبْلَ أَنْ تَزِيغَ الشَّمْسُ أَخَّرَ الظُّهْرَ إِلَى وَقْتِ الْعَصْرِ، ثُمَّ نَزَلَ فَجَمَعَ بَيْنَهُمَا، فَإِنْ زَاغَتِ الشَّمْسُ قَبْلَ أَنْ يَرْتَحِلَ صَلَّى الظُّهْرَ ثُمَّ رَكِبَ‏.‏

English translation

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

Reference: Sahih al-Bukhari 1112, Book of Shortening the Prayers (At-Taqseer). English translation by Dr. Muhammad Muhsin Khan.