Well if Josephus says so it must be true.
Yet Paul says :
Romans 4:11-12 ASV
and he (Abraham),received the sign of circumcision, a seal of the righteousness of the faith which he had while he was in uncircumcision: that he might be the father of all them that believe,though they be in uncircumcision, that righteousness might be reckoned unto them; [12] and the father of circumcision to them who not only are of the circumcision, but who also walk in the steps of that faith of our father Abraham which he had in uncircumcision.
Romans 11:16-17 ASV
And if the first-fruit is holy, so is the lump: and if the root is holy, so are the branches. [17] But if some of the branches were broken off, and thou, being a wild olive, wast grafted in among them, and didst become partaker with them of the root of the fatness of the olive tree;
Yet Paul says :
Romans 4:11-12 ASV
and he (Abraham),received the sign of circumcision, a seal of the righteousness of the faith which he had while he was in uncircumcision: that he might be the father of all them that believe,though they be in uncircumcision, that righteousness might be reckoned unto them; [12] and the father of circumcision to them who not only are of the circumcision, but who also walk in the steps of that faith of our father Abraham which he had in uncircumcision.
Romans 11:16-17 ASV
And if the first-fruit is holy, so is the lump: and if the root is holy, so are the branches. [17] But if some of the branches were broken off, and thou, being a wild olive, wast grafted in among them, and didst become partaker with them of the root of the fatness of the olive tree;