Musnad Ahmad 30:220

I heard Sufyan say: "If the servant prepares the food for one of you, let him seat him and let him eat with him. If he does not do so, then let him take a morsel, let him coat it in it [the food], and let him hand it to him." And its chain of narration was read to him: I heard Abu al-Zinad, from al-A'raj, from Abu Hurayrah, from the Prophet, may God bless him and grant him peace.