"In reply to the statement that Christ was the Son of David, Jesus said, “How then doth David in Spirit [the Spirit of Inspiration from God] call Him Lord, saying, The Lord said unto my Lord, Sit Thou on My right hand, till I make Thine enemies Thy footstool? If David then call Him Lord, how is He his son? And no man was able to answer Him a word, neither durst any man from that day forth ask Him any more questions.” DA 609.1"
The EGW passage is a direct quote from Psalms 110:1.