Romans 7:21-23: (Remember, this is God's apostle saying this): " So I find it to be a law that when I want to do right, evil lies close at hand. 22 For I delight in the law of God, in my inner being, 23 but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members."
So, Paul, a Christian and Apostle, acknowledges that he is "captive" (present tense) to the "law of sin" that "dwells" (also, present tense) within him.
Paul the Apostle, again, asserts Peter, a fellow apostle of God, has sinned and so Paul publicly reprimands him - even tells him he has done wrong (has sinned!) - in Galatians 2 Paul condemns and publicly reprimands Peter for his sinful behavior : "But when Cephas came to Antioch, I opposed him to his face, because he stood condemned." Further, Paul states of Peter and the other Christians sinning along with Peter: "And the rest of the Jews acted hypocritically along with him, so that even Barnabas was led astray by their hypocrisy. 14 But when I saw that their conduct was not in step with the truth of the gospel, I said to Cephas before them all, “If you, though a Jew, live like a Gentile and not like a Jew, how can you force the Gentiles to live like Jews?”
So, Paul asserts an apostle of God and other Christians amongst them have conduct that was "not in step with the truth of the Gospel - in other words, they've sinned, and he says they are "condemned" of this - not meaning they aren't saved - clearly, they are. But Paul is saying saved people, even an apostle, have sinned.
1 John 1, the Apostle says: " If we say we have no sin, we deceive ourselves, and the truth is not in us." So John is including himself with the words "ourselves" and "us."
Was Peter the Disciple saved when he denied Jesus three times? But well before this, Peter had already been saved, as He believe who Jesus was (God! The Messiah!): Peter was the first to call Jesus the Son of the Living God – the Messiah (Mark 8:29, Luke 9:20, Matt. 16:16-17). Ah, but then he cursed as Jesus was being interrogated, denied knowing him - wasn't that SIN???
Last, jpbg, when you do something wrong, what do you call it? John says if we deny such isn't sin, then "the truth is not in us." And I'm assuming you aren't perfect?