Exodus14and Deuteronomy.15Beginning with the Old Testament, the sacred books refer to the "ten
The "ten words" sum up and proclaim God's law: "These words the Lord spoke to all your assembly at the mountain out of the midst of the fire, the cloud, and the thick darkness, with a loud voice; and he added no more. And he wrote them upon two tables of stone, and gave them to me." For this reason these two tables are called "the Testimony." In fact, they contain the terms of the covenant concluded between God and his people. These "tables of the Testimony" were to be deposited in "the ark."
Source: Catechism of the Catholic Church (Vatican.va)