Sahih Bukhari Volume 2, Book 20, Hadith Number 210.
Narated By Az-Zuhri : Salim told me, “‘Abdullah bin ‘Umar said, ‘I saw Allah’s Apostle delaying the Maghrib prayer till he offered it along with the Isha prayer whenever he was in a hurry during the journey.’ ” Salim said, “Abdullah bin Umar used to do the same whenever he was in a hurry during the journey. After making the call for Iqama, for the Maghrib prayer he used to offer three Rakat and then perform Tasllm. After waiting for a short while, he would pronounce the Iqama for the ‘Isha’ prayer and offer two Rakat and perform Taslim. He never prayed any Nawafil in between the two prayers or after the ‘Isha’ prayers till he got up in the middle of the night (for Tahajjud prayer).”