Musnad Abu Ya'la al-Mawsili 6:43

Abu Khaythama narrated to us, Waki' narrated to us, Usama bin Zayd narrated to us, from Muhammad bin 'Abd al-Rahman bin Abi Labiba, from Sa'd bin Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of provision is that which suffices, and the best of remembrance is the hidden [one]."