"Through being overcome with sleep, the disciples heard little of what passed between Christ and the heavenly messengers. Failing to watch and pray, they had not received that which God desired to give them,—a knowledge of the sufferings of Christ, and the glory that should follow. They lost the blessing that might have been theirs through sharing His self-sacrifice. Slow of heart to believe were these disciples, little appreciative of the treasure with which Heaven sought to enrich them. DA 425.1"
"Watch and pray, that ye enter not into temptation: the spirit indeed is willing, but the flesh is weak."
Both passages discuss the importance of watching and praying, and the consequences of failing to do so. While not a direct quote, the theme is clearly present.
"Yet they received great light. They were assured that all heaven knew of the sin of the Jewish nation in rejecting Christ. They were given a clearer insight into the work of the Redeemer. They saw with their eyes and heard with their ears things that were beyond the comprehension of man. They were “eyewitnesses of His majesty” ( 2 Peter 1:16 ), and they realized that Jesus was indeed the Messiah, to whom patriarchs and prophets had witnessed, and that He was recognized as such by the heavenly universe. DA 425.2"
"For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty."
Ellen White directly references 2 Peter 1:16 in this passage.
"While they were still gazing on the scene upon the mount, “a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is My beloved Son, in whom I am well pleased; hear ye Him.” As they beheld the cloud of glory, brighter than that which went before the tribes of Israel in the wilderness; as they heard the voice of God speak in awful majesty that caused the mountain to tremble, the disciples fell smitten to the earth. They remained prostrate, their faces hidden, till Jesus came near, and touched them, dispelling their fears with His well-known voice, “Arise, and be not afraid.” Venturing to lift up their eyes, they saw that the heavenly glory had passed away, the forms of Moses and Elijah had disappeared. They were upon the mount, alone with Jesus. DA 425.3"
"While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him."
The EGW passage directly quotes and elaborates on Matthew 17:5, including the bright cloud, the voice from the cloud declaring Jesus as the beloved Son, and the disciples' reaction. This is a clear and direct allusion.
"Then a cloud covered the tent of the congregation, and the glory of the Lord filled the tabernacle."
Both passages describe a cloud and the glory of God, but the context and specific details differ. The EGW passage refers to the Transfiguration, while the Exodus passage refers to the tabernacle. The connection is thematic, not a direct allusion.