It is said (ειρητα). 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" (γεγραπτα). 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 ουκ, a common prohibition. Jesus points out to the devil that testing God is not trusting God (Plummer).