In 1904 Ellen White wrote:
"Messages of every order and kind have been urged upon Seventh-day Adventists, to take the place of the truth which, point by point, has been sought out by prayerful study, and testified to by the miracle-working power of the Lord. But the waymarks which have made us what we are, are to be preserved, as God has signified through His Word and the testimony of His Spirit. He calls upon us to hold firmly, with the grip of faith, to the fundamental principles that are based upon unquestionable authority." 1SM 208
"The enemy of souls has sought to bring in the supposition that a great reformation was to take place among Seventh-day Adventists, and that this reformation would consist in giving up the doctrines which stand as the pillars of our faith, and engaging in a process of reorganization. Were this reformation to take place, what would result? The principles of truth that God in His wisdom has given to the remnant church, would be discarded. Our religion would be changed. The fundamental principles that have sustained the work for the last fifty years would be accounted as error. A new organization would be established. Books of a new order would be written. A system of intellectual philosophy would be introduced." 1SM 204
To what fundamental principles was she referring? In 1872 a pamphlet was printed on the steam press of the Seventh-day Adventist Publishing Association in Battle Creek, Michigan. It was entitled, A Declaration of the Fundamental Principles Taught and Practiced by the Seventh-day Adventists. As stated in its opening paragraph, it was "a brief statement of what is, and has been, with great unanimity, held by them." It had 25 points.
In 1874 James White founded the periodical Signs of the Times. The very first issue, Volume I, Number I, June 4, 1874, featured the church's declaration of Fundamental Principles just as it had appeared in the earlier pamphlet. Again, the description was included that this doctrinal statement represented "what is, and has been, with great unanimity," held by "our people."
In the years 1889, 1905, and 1907-1914, the same list of Fundamental Principles was included in the Seventh-day Adventist Yearbook. It was prefaced with this comment:
"Seventh-day Adventists have no creed but the Bible; but they hold to certain well-defined points of faith, for which they feel prepared to give a reason 'to every man that asketh' them. The following propositions may be taken as a summary of the principle features of their religious faith, upon which there is, so far as is known, entire unanimity throughout the body."
There can be no doubt, then, that these long-published Fundamental Principles were what Ellen White had in mind when in 1904 she warned against discarding "the fundamental principles that have sustained the work" for so many years.
Below is a link to a digitized archive of this historically important doctrinal summary. You will notice that care is taken to dispel any notion that early Seventh-day Adventists viewed their statement of beliefs as a standard of disciple. It was merely informational.
A Declaration of the Fundamental Principles of the Seventh-day Adventists