Musnad Ahmad 27:1894

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Salim, from Ibn 'Umar, who said: "When the Messenger of Allah, peace and blessings of Allah be upon him, was in a hurry in his travel, he would combine the Maghrib and the 'Isha prayers."