"against Christ. When the prince of this world shall be judged, and all who have united with him shall share his fate, the whole universe as witnesses to the sentence will declare, “Just and true are Thy ways, Thou King of saints.” Revelation 15:3 . PP 79.1"
"And they sing the song of Moses the servant of God, and the song of the Lamb, saying, Great and marvellous are thy works, Lord God Almighty; just and true are thy ways, thou King of saints."
EGW directly quotes Revelation 15:3, making it a clear and explicit allusion.