הלכה אויף דברים 5:6

To know this matter is a mandatory commandment, saying: "I am the Lord thy God" (Ex. 20,2); therefore, whosoever supposes that there is another god besides This One, (1) violates a prohibitive commandment, saying: "Thou shalt have no other gods before me" (Ibid. –3), and is an atheist, denying the great principle upon which everything depends.

To know that there is a God, as it is said, “I am the Lord, thy God” (Ex. 20:2; Deut. 5:6).

The first of the negative precepts is not to entertain the idea that there is any god but the Eternal, as it is said, “Thou shalt have no other gods before me” (Ex. 20:3).