The Prophet ﷺ, when he set out on a journey before the sun had passed its zenith, would delay the noon prayer until the time of the afternoon prayer, then combine the two. But if the sun had already passed its zenith, he would pray the noon prayer first and then mount his ride.
كان النبي ﷺ إذا ارتحل قبل أن تزيغ الشمس أخر الظهر إلى وقت العصر، ثم يجمع بينهما. وإذا زاغت صلى الظهر ثم ركب.
Bukhari narrated it in the chapter on shortening the prayer (1112), and Muslim in the chapter on the prayer of travelers (704), both from Qutayba bin Saeed, from Mufaddal bin Fadala, from Aqeel, from Ibn Shihab, from Anas, as mentioned. In a narration by Muslim from another route, from Aqeel bin Khalid, "When he wanted to combine the two prayers while traveling, he would delay Dhuhr until the beginning of the time of Asr, then combine them." And in another narration by Muslim from another route, from Aqeel, "When travel pressed upon him, he would delay Dhuhr until the beginning of the time of Asr and combine them, and he would delay Maghrib so as to combine it with Isha when twilight disappeared."Ishaq bin Rahawayh narrated it with his chain from Anas, who said, "When the Messenger of Allah was traveling and the sun had passed its zenith, he would pray Dhuhr and Asr together, then set out." Bayhaqi narrated it (3/162) through the route of Ishaq bin Rahawayh. Nawawi said in Majmu (4/372), "Its isnad is sahih." Hafiz confirmed this in Talkhis (2/49) and spoke at length on tracing its sources. It shows the permissibility of combining prayers by bringing the later one forward.As for what Bazzar narrated, in Kashf Astar (688), through the route of Muhammad bin Ishaq, from Hafs, who said, "When Anas wanted to combine the two prayers while traveling, he would delay Dhuhr to the end of its time and pray it, then pray Asr at the beginning of its time, and he would pray Maghrib at the end of its time, and pray Isha at the beginning of its time, and he would say, 'This is how the Messenger of Allah used to combine the two prayers while traveling.'" Bazzar said, "We do not know of anyone who corroborated Hafs bin Ubaydullah in this narration, and Zuhri narrated it differently from what Hafs narrated." End of quote. Haythami said in Majma (2/160), "Bazzar narrated it, and in it is Ibn Ishaq, who is trustworthy but a mudallis." End of quote.