(Exodus 23:19) "You shall not cook a kid in its mother's milk": R. Shimon says: Why is this written in three places? (here, (Exodus 34:26) and (Devarim 14:21). They correspond to the three covenants that the Holy One Blessed be He forged with Israel: one in Chorev, one Arvoth Moav, and one in Mount Gerizim and Mount Eival.