Musnad Ahmad 31:536

Ya'mar ibn Bishr narrated to us, Abdullah informed us, Sa'id ibn Abi Ayyub informed us, Abdullah ibn al-Walid narrated to us, from Abu Sulayman al-Laythi, from Abu Sa'id al-Khudri, from the Prophet (peace and blessings of Allah be upon him), who said: "The likeness of the believer and the likeness of faith is like the likeness of a horse in its tether; it wanders, then returns to its tether. And indeed, the believer becomes heedless, then returns to faith. So feed your food to the pious, and bestow your kindness upon the believers." Abdullah said: My father said: Abu Abd al-Rahman al-Muqri narrated it to us, "and this is more complete."