Sayyiduna Ibn Umar (may Allah be pleased with them both) said: I saw the Messenger of Allah (peace and blessings be upon him) that when he (peace and blessings be upon him) was in a hurry to travel on a journey, he (peace and blessings be upon him) would delay Maghrib until he combined it with the Isha prayer.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13051