It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) used to combine the Zuhr and Asr prayers, and the Maghrib and Isha prayers, while travelling, when he (peace and blessings be upon him) was neither pursuing an enemy nor being pursued by an enemy.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11322