Let us see how the Bible answers your question. In Luke 4:16 (NASB) the Bible says of Jesus, And He come to Nazareth, were He had been brought up; and as was His custom, He entered the synagogue on the Sabbath, and stood up to read. The Bible says that it was Jesus' custom to keep the Sabbath holy according to the commandments. Now which day did Jesus keep holy as the Sabbath? Well, Jesus was a Jew and all Jews of his time kept the Saturday holy just as they do today. This is well documented historically. Ask any Jew today which day is the biblical Sabbath and they will tell you that Saturday is that day. Is it possible that the original seventh day of creation week could have gotten lost, and that we no longer can know which day it was? Again we have to go back to the Bible for the answer. When God brought the Israelites out of Egypt by Moses, He gave them the Ten Commandments as the foundation of their government. Included in that Ten Commandments is the fourth commandment which bids the people to Remember the Sabbath day to keep it holy. Now we know that the people that Moses brought out of Egypt became the Jewish Nation. The Jews of today like to class themselves as descendants of the people that Moses brought out of Egypt. The same Sabbath that the people of Moses' time kept is the one that the modem Jew now keeps. Historically we cannot dispute this. And we know that day is the Saturday. Here is another point. The day before the Sabbath is known as the Preparation Day; this day we know to be the Friday, the same day we call Friday today. The day that follows Friday is Saturday. The Jews keep this day as their Sabbath. It is also interesting to know that over 5 languages on this earth call the Seventh day the Sabbath. Why do these languages do so? It is obvious that the people who used these languages must have named the seventh day Sabbath because of the creation story. The knowledge that God rested on the Seventh day and blessed it and sanctified it must have been passed along to them. Most scholars today would agree that historically we can clearly show that Saturday is the biblical Sabbath. God bless.