Musnad Abu Ya'la al-Mawsili 153:116

Ishaq ibn Abi Isra'il narrated to us, Sufyan narrated to us, al-Zuhri narrated to us, from Salim, from his father, that the Prophet (peace and blessings of Allah be upon him), when he was in a hurry in his travel, would combine the Maghrib and Isha prayers.