Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) reports this saying of the Prophet (peace and blessings be upon him): "A slave has three rights over his master: that he does not hurry him in his prayer, that he does not make him get up while he is eating, and that he feeds him until he is fully satisfied."
Imam Tabarani recorded it in al-Mu'jam al-Saghir; its chain contains narrators whom I do not know, and a narrator, Abd al-Samad bin Ali, who is da'if (weak). Hadiths about treating a servant well have already passed earlier in the Book of Emancipation (Kitab al-Itq).