"The time has come to make decided efforts in places where the truth has not yet been proclaimed. How shall the Lord's work be done? In every place that is entered, a solid foundation is to be laid for permanent work. The Lord's methods are to be followed. It is not for you to be intimidated by outward appearances, however forbidding they may be. It is for you to carry forward the work as the Lord has said it should be carried. Preach the word, and the Lord by His Holy Spirit will send conviction to the minds of the hearers. The word is, “They went forth, and preached everywhere, the Lord working with them, and confirming the word with signs following.” [ Mark 16:20 .] GW 354.3"
"And they went forth, and preached every where, the Lord working with them, and confirming the word with signs following. Amen."
Ellen White directly references Mark 16:20 in this passage.