I think this is the verse you're thinking of. My understanding based on the context is that we do not need a teacher because the Holy Spirit points the hearts of believers to see and accept Christ as the Son of God and savior.
1 John 2:19-27
They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us. But you have an anointing from the Holy One, and all of you know the truth. I do not write to you because you do not know the truth, but because you do know it and because no lie comes from the truth. Who is the liar? It is the man who denies that Jesus is the Christ. Such a man is the antichrist--he denies the Father and the Son. No one who denies the Son has the Father; whoever acknowledges the Son has the Father also. See that what you have heard from the beginning remains in you. If it does, you also will remain in the Son and in the Father. And this is what he promised us--even eternal life. I am writing these things to you about those who are trying to lead you astray. As for you, the anointing you received from him remains in you, and you do not need anyone to teach you. But as his anointing teaches you about all things and as that anointing is real, not counterfeit--just as it has taught you, remain in him.
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