this is an Incident of Abrahim Peace be upon him
Abrahim (peace be upon him)was prophet who had come before christanity and ISLAM
he kept a practice to Always eat and share his food with a guest, once a person 70 years old had come who did not know God. when they were starting to eat
Abrahim(Peace be upon him ) asked him to start food in the name of god
he asked what to start with? and what is Allah ?
he got upset and said One who Does not know Allah he cannot eat with me , go away
he waked away
Allah send a message to Abrahim peace be upon him- he did not know me for 70 years and still i have been feeding him all these years, he came to you once and u drove him away ?
Abrahim(peace be upon him) ran immedieatly bare feet to search for that man, and invited him again, he asked why did u drive me away.
he said i recieved such and such message in response to my act. and he was from then the follower of Abrahim peace be upon him.