It is said (eirhtai). Perfect passive indicative, stands said, a favourite way of quoting Scripture in the N.T. In Matthew 4:7 we have the usual "it is written" (gegraptai). Here Jesus quotes Deuteronomy 6:16 . Each time he uses Deuteronomy against the devil. The LXX is quoted. It is the volitive future indicative with ouk, a common prohibition. Jesus points out to the devil that testing God is not trusting God (Plummer).