Sahih Bukhari Volume 4, Book 52, Hadith Number 244.

Narated By Aslam : While I was in the company of ‘Abdullah bin ‘Umar on the way to Mecca, he received the news of the severe illness of Safiya bint Abi Ubaid (i.e. his wife), so he proceeded at greater speed, and when the twilight disappeared, he dismounted and offered the Maghrib and ‘Isha ‘prayers together and said, ” I saw the Prophet delaying the Maghrib prayer to offer it along with the ‘Isha’ when he was in a hurry on a journey.”