Musnad Ahmad 30:3436

Yazid narrated to us, Ibn Abi Dhi’b informed us, from ‘Ajlan, and Isma’il ibn ‘Umar said: Ibn Abi Dhi’b narrated to us—the meaning—from ‘Ajlan, from Abu Hurairah, that the Prophet, peace and blessings of Allah be upon him, said regarding the slave: "He prepares your food and takes care of it, so invite him [to eat]. If he refuses, then feed him by your hand. And when you strike them, do not strike them on their faces."