Exodus 24:4

24:4 and Moses wrote down all the words of the Lord. Early in the morning he built an altar at the foot of the mountain and arranged twelve standing stones – according to the twelve tribes of Israel.

Exodus 34:24

34:24 For I will drive out the nations before you and enlarge your borders; no one will covet your land when you go up to appear before the Lord your God three times in the year.