Moses was on Mount Sinai for two separate periods of 40 days and 40 nights each time.

• The first time, Moses stayed on the mountain for 40 days and nights to receive the Ten Commandments from God. When he came down, he found the Israelites worshipping a golden calf, which led him to break the first set of tablets

• After this, God instructed Moses to chisel out two new stone tablets, and Moses went back up the mountain alone for another 40 days and nights. During this second stay, Moses received a repetition of the covenant and the Ten Commandments, again without eating or drinking

In total, Moses spent 80 days on Mount Sinai across these two significant visits, each lasting 40 days and nights. These events are described primarily in the book of Exodus chapters 24 and 34