Man is not perfect so where is that in the Bible?
That’s correct.
Man is NOT perfect. Even saved people are not perfect.
What they are is DECLARED perfect by God as He judicially pardons our sin since it was paid for by Jesus.
When we stand before God, we can point to Jesus and say, “He did it. He paid my penalty.” and God accepts that payment on our behalf and judicially pardons us from any further payment of the penalty ourselves.