Acts 5:39

But if it is of God (ei de ek qeou estin). The second alternative is a condition of the first class, determined as fulfilled, ei with the present indicative. By the use of this idiom Gamaliel does put the case more strongly in favor of the apostles than against them. This condition assumes that the thing is so without affirming it to be true. On the basis of this alternative Gamaliel warns the Sanhedrin that they cannot "overthrow" (katalusai) these men for they in that case must "overthrow" God, lest haply ye be found (mh pote--ureqhte, negative purpose with first aorist passive subjunctive) even to be fighting against God (kai qeomacoi, late adjective from qeo and macomai, in LXX and here only in the N.T.).