Salim narrates from Abdullah bin Umar (may Allah be pleased with them both) that 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 on a journey, he would delay Maghrib and combine it with Isha. Salim said: When Abdullah bin Umar (may Allah be pleased with them both) was in haste, he would do the same. He would have the iqamah given for Maghrib and pray three rak'ahs, then end with the salam; then, after waiting only a little, he would have the iqamah given for Isha and pray two rak'ahs, then end with the salam. He would not pray any voluntary rak'ah between the two prayers, nor a single rak'ah after Isha, until he rose in the depth of the night for the night prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5537