Sahih Muslim Book 27, Hadith 65
When a slave looks to the welfare of his master and worships Allah well, he has two rewards for him.
When the slave of anyone amongst you prepares food for him and he serves him after having sat close to (and undergoing the hardship of) heat and smoke, he should make him (the slave) sit along with him and make him eat (along with him), and if the food seems to run short, then he should spare some portion for him (from his own share) - (another narrator) Dawud said:" i. e. a morsel or two". 4097
This hadith has been narrated on the authority of Ibn 'Umar through another chain of transmitters.