Musnad Abu Ya'la al-Mawsili 42:429

On the authority of Abu Sa'id al-Khudri, he said: I said, "O Messenger of Allah, may Allah bless him and grant him peace, which act of worship is highest in rank before Allah on the Day of Resurrection?" He said, "Those who remember Allah much." I said, "O Messenger of Allah, even the warrior in the way of Allah?" He said, "If he were to strike the disbelievers and the polytheists with his sword until it breaks and becomes stained with blood, the one who remembers Allah would still be better than him."