Seventh-day Sabbath observance among Christians did not begin with Adventism. Small Seventh Day Baptist congregations had kept Saturday as the Sabbath in England since the 1650s and in colonial Rhode Island since the 1670s, reading the fourth commandment as a permanent creation ordinance never abrogated in the New Testament, centuries before the movement that would carry the practice to a much larger audience existed.
That transfer happened through one woman. Rachel Oakes Preston, a Seventh Day Baptist living in Washington, New Hampshire, shared her congregation's Sabbath conviction with local Millerite believers, followers of William Miller's prediction that Christ would return in 1844, in the months after Miller's expected date passed without the return, an episode Adventists call the Great Disappointment. Among those persuaded was Thomas M. Preston, and through the New Hampshire Millerites the practice reached the movement's emerging leadership, including Ellen G. White, whose subsequent visions and writings confirmed and helped establish it as settled doctrine.
The believers who organized formally in 1863 took the name Seventh-day Adventist specifically to name both convictions together, the seventh-day Sabbath and the imminent advent of Christ, making the Sabbath the first word of the denomination's own name rather than an incidental practice.