Seventh Day Adventist Sabbath day observers base their faith and practise on the following (not exclusively of course)...
KJV Genesis 2:1-3
1 Thus the heavens and the earth were finished, and all the host of them.
2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.
3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
KJV Exodus 20:8
8 Remember the sabbath day, to keep it holy.
KJV Isaiah 58:10-14
10 And if thou draw out thy soul to the hungry, and satisfy the afflicted soul; then shall thy light rise in obscurity, and thy darkness be as the noonday:
11 And the LORD shall guide thee continually, and satisfy thy soul in drought, and make fat thy bones: and thou shalt be like a watered garden, and like a spring of water, whose waters fail not.
12 And they that shall be of thee shall build the old waste places: thou shalt raise up the foundations of many generations; and thou shalt be called, The repairer of the breach, The restorer of paths to dwell in.
13 If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day; and call the sabbath a delight, the holy of the LORD, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
14 Then shalt thou delight thyself in the LORD; and I will cause thee to ride upon the high places of the earth, and feed thee with the heritage of Jacob thy father: for the mouth of the LORD hath spoken it.
KJV Matthew 12:8
8 For the Son of man is Lord even of the sabbath day .
KJV Matthew 12:11-12
11 And he said unto them, What man shall there be among you, that shall have one sheep, and if it fall into a pit on the sabbath day, will he not lay hold on it, and lift it out?
12 How much then is a man better than a sheep? Wherefore it is lawful to do well on the sabbath days.
KJV Luke 24:25-27
25 Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken:
26 Ought not Christ to have suffered these things, and to enter into his glory?
27 And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.
KJV Revelation 14:6-12
6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,
7 Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters.
8 And there followed another angel, saying, Babylon is fallen, is fallen, that great city, because she made all nations drink of the wine of the wrath of her fornication.
9 And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,
10 The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:
11 And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name.
12 Here is the patience of the saints: here are they that keep the commandments of God, and the faith of Jesus.