(16) باب إِذَا ارْتَحَلَ بَعْدَ مَا زَاغَتِ الشَّمْسُ صَلَّى الظُّهْرَ ثُمَّ رَكِبَ
Narrated Anas bin Malik:
Whenever the Prophet (ﷺ) started on a journey before noon, he used to delay the Zuhr prayers 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
In-book reference: Book 18, Hadith 32
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 20, Hadith 213