Musnad Abu Ya'la al-Mawsili 42:359

Zuhayr narrated to us, Abdullah bin Yazid narrated to us, Sa'id bin Abi Ayyub narrated to us, Abdullah bin al-Walid narrated to me, from Abu Sulayman al-Taymi, from Abu Sa'id al-Khudri, from the Prophet, may God bless him and grant him peace, who said: "The likeness of the believer and the likeness of faith is like the 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."