Deuteronomy 6:4

The Lord our God is one Lord. Literally, “Jehovah our God, Jehovah [is] One.” In striking contrast to the nations about them, who were polytheists, the Hebrews believed in one true God. This profession of faith has been the watchword of the Hebrew race for more than 3,000 years (see Mark 12:29). The apostle Paul states the same truth as a tenet of Christianity (1 Cor. 8:4-6; Eph. 4:4-6).

Prior to the discovery of the Dead Sea scrolls, the oldest extant Hebrew manuscript of any part of the OT was the Nash Papyrus, of the 1st century B.C., which contains the Decalogue and Deut. 6:4, 5.