The 4th commandment is about the sabbath. What is the true sabbath? I've been taught it's Sunday?

Please show where in the Bible it says the Passover is the Christian Sabbath.Mat_5:17  "Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill. If he made the Law about adultery stronger by saying if a man lust after a woman he has committed adultery in his heart. why would He diminish the Sabbath day then say He said He was Lord of the Sabbath. The Sabbath He kept as it was made after the earth was finished, the same Sabbath the Jews kept but accused Jesus of breaking, when He healed, and did good on the Sabbath. The same Sabbath that the pagan Romans turned against to establish their worship of the sun, and institute their day to worship the sun as the christian Sabbath. This sound like Satan opposing God's word, to create confusion. We must worship God , in Spirit and in TRUTH. Gen 2:2  And on the seventh day God ended His work which He had done, and He rested on the seventh day from all His work which He had done. 
Gen 2:3  Then God BLESSED the seventh day and SANCTIFIED it, because in it He rested from all His work which God had created and made.  Not written that God did that to any other day of the week.