From Sahih Bukhari (Hadith 1111):
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: Bukhari 1111