Gamaliel’s counsel.
”But a Pharisee named Gamaliel, a teacher of the Law respected by all the people, stood up in the Council and gave orders to put the men out for a short time. And he said to them, ‘Men of Israel, take care what you propse to do to these men. … So in the present case, I say to you, stay away from these men and let them alone, for if this plan or action is of men, it will be overthrown; but if it is of God you will not be able to overthrow them; or else you may even be found fighting against God.’”
(Acts 5:34-35, 38-39)
It hasn’t been overthrown. They are fighting against God.
”They took his advice; and after calling the apostles in, they flogged them and ordered them not to speak in the name of Jesus, and then released them.”
(Acts 5:40)
They can’t speak to the Jews using the doctrinal authority of the New Testament as they lived it?
”So then they went on their way from the presence of the Council, rejoicing that they had been considered worthy to suffer shame for his name. And every day, in the temple and from house to house, they kept right on teaching and preaching Jesus the Messiah.”
(Acts 5:41-42)
I must use New Testament quotes as a source of doctrinal authority when speaking to a Jew (and when speaking to non-Jews.)