Musannaf Ibn Abi Shayba 33:755

Abdullah ibn Idris narrated to us, from his paternal uncle, from Kardus, who said: He used to preach to us in the morning and in the evening. He would say: "Indeed, Paradise is not attained except by working for it. Mix desire with fear, persist in righteousness, and fear Allah with sound hearts and righteous deeds." And he would frequently say: "Whoever fears, travels by night."