Zayd bin Aslam (may Allah have mercy on him) narrates from his father that he said: I was with Abdullah bin Umar (may Allah be pleased with them both) on the road to Makkah. News reached him of the severe illness of Safiyyah bint Abi Ubayd (may Allah be pleased with her), so he travelled fast until the twilight had disappeared. Then he dismounted and prayed Maghrib and Isha, combining the two. Then he said: I saw the Messenger of Allah (peace and blessings be upon him): "When he (peace and blessings be upon him) was in haste to travel, he would delay Maghrib and combine the two," that is, Isha and Maghrib.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5517