In the Ten Commandments, which day is called a Sabbath to the LORD?

Answer: The seventh day

Six days you shall labor, but the seventh day is a Sabbath to the LORD, on which no one may do any work.

“Remember the Sabbath day by keeping it holy. Six days you shall labor and do all your work, but the seventh day is a Sabbath to the LORD your God, on which you must not do any work—neither you, nor your son or daughter, nor your manservant or maidservant or livestock, nor the foreigner within your gates.”— Exodus 20:8-10 (BSB)