Is your answer Peter was saved by his gospel or saved by Paul's gospel? I can't tell what your answer is. Sorry.
That's nothing - if we go back further, it is evident, say, in John 1, that such as Nathaniel (one of the Twelve Apostles) were saved before even meeting, let alone believing, that Jesus was their Prophesied Christ.
Such were saved under "the righteousness of the law."
In other words, those Israelites who not only kept the Law, but did so from the heart - "not as pleasing men" (mere outward performance) "but as pleasing God."
Luke 1:5 There was in the days of Herod, the king of Judaea, a certain priest named Zacharias, of the course of Abia: and his wife was of the daughters of Aaron, and her name was Elisabeth. 1:6 And they were both righteous before God, walking in all the commandments and ordinances of the Lord blameless.
With His arrival, to their believing their Law and their Prophets would have then been added the requirement that they believe that Jesus was the Christ their Law did say would come...
Acts 7:51 Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye. 7:52 Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers: 7:53 Who have received the law by the disposition of angels, and have not kept it.
Romans 2:24 For the name of God is blasphemed among the Gentiles through you, as it is written. 2:25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.
2:28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
John 5:44 How can ye believe, which receive honour one of another, and seek not the honour that cometh from God only? 5:45 Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. 5:46 For had ye believed Moses, ye would have believed me: for he wrote of me. 5:47 But if ye believe not his writings, how shall ye believe my words?
Rom. 5:8
Acts 17:11,12