Musnad Ahmad 26:693

Waki' narrated to us, from Isra'il, from Abu Ishaq, from Abu 'Ubaydah, from 'Abdullah, who said: I said: "O Messenger of Allah, which deed is best?" He said: "Prayer at its time." He said: I said: "Then what?" He said: "Kindness to parents." He said: I said: "Then what?" He said: "Jihad in the way of Allah, the Mighty and Majestic." And had I asked him for more, he would have added more for me.