Musannaf Ibn Abi Shayba 33:757

Muhammad ibn Bishr narrated to us, he said: Mis'ar narrated to us, he said: Habib ibn Abi Thabit narrated to us, from Yahya ibn Ja'dah, he said: It used to be said: "Work while you are apprehensive, and leave work while you desire it. A small righteous deed that you persist upon [is better]."