Judaism, Christianity, and Islam are all monotheistic religions. Meaning, the followers only worship one God.
In Judaism, in the Ten Commandments, it states "you shall have no other gods before me" (Exodus 20:3).
Christianity, which branches off of Judaism, in a way, also uses the Ten Commandments.
The core beliefs of Islam can be summed up in the Five Pillars of Islam. The first pillar is shahada, which states "there is no god but Allah, and Muhammad is the messenger and prophet of Allah".