Although He, as Jehovah, did cause Moses to write down His Words, it was to that written Word that He referred to in reproving Satan, thus authorizing its standing alone as irrefutable and eternal. Mt. 4:4 in Gk, "It is written" is in the perfect tense, not "It was written." Most certainly Jesus did quote from memory, of what He had caused to be written. He also referred to the Word as the "hrema" the spoken word, as having come out of the mouth of God (that is, of His Own mouth), IIRC.
Matthew 5:18
For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.