Musannaf Ibn Abi Shayba 3:5862

Waki’ narrated to us, he said: Sufyan narrated to us, from Abu Qays, from Hudhayl ibn Sharhabil al-Awdi, he said: The Messenger of Allah (may Allah bless him and grant him peace) combined the Dhuhr and ‘Asr prayers, and the Maghrib and ‘Isha prayers, while traveling.