From Sahih Bukhari (Hadith 1112):
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: Bukhari 1112