The Messenger of Allah ﷺ said, "When the servant of one of you brings him his food, having spared him its heat and labor, then if he does not seat him with him to eat, let him hand him a morsel of it."
حدثنا عفان قال حدثنا حماد قال أخبرنا عمار بن أبي عمار قال سمعت
إن رسول الله ﷺ قال إذا جاء خادم أحدكم بطعامه قد كفاه حره وعمله فإن لم يقعده معه ليأكل فليناوله أكلة من طعامه
Its chain of transmission is sahih. Bukhari related it, 5/181, no. 2557, in Fath al-Bari, in the chapter on manumission, "If one of you brings his servant." Muslim also related it, 3/1284, no. 1663, in the chapter on oaths, "Feeding the slave." And Abu Dawud related it, 3/365, no. 3846, in the chapter on foods, "The servant eats with his master."