Genesis 26:30-31. He made them a feast, and they did eat and drink. And they rose up betimes... and sware one to another.
It was customary among the Hebrews, and also among the heathen nations, to eat together when entering into a covenant. When Jacob made his covenant with Laban he made a feast for his brethren (Gen. 31:54). Many allusions to this custom are made by classical writers.