"God will not break His covenant, nor alter the thing that has gone out of His lips. His word will stand fast forever as unalterable as His throne. At the judgment this covenant will be brought forth, plainly written with the finger of God, and the world will be arraigned before the bar of Infinite Justice to receive sentence. PK 187.1 Today, as in the days of Elijah, the line of demarcation between God's commandment-keeping people and the worshipers of false gods is clearly drawn. “How long halt ye between two opinions?” Elijah cried; “if the Lord be God, follow Him: but if Baal, then follow him.” 1 Kings 18:21 . And the message for today is: “Babylon the great is fallen, is fallen.... Come out of her, My people, that ye be not partakers of her sins, and that ye receive not of her plagues. For her sins have reached unto heaven, and God hath remembered her iniquities.” Revelation 18:2, 4, 5 . PK 187.2"
"And Elijah came unto all the people, and said, How long halt ye between two opinions? if the Lord be God, follow him: but if Baal, then follow him. And the people answered him not a word."
Ellen White directly references 1 Kings 18:21 in this passage.
"My covenant will I not break, nor alter the thing that is gone out of my lips."
EGW directly quotes and references Psalm 89:34, emphasizing the unchangeable nature of God's covenant.