Leviticus 5:18

‎ לאשם בערכך [HE SHALL BRING A RAM …] ACCORDING TO THE VALUATION FOR A GUILT OFFERING — i. e. according to the value stated above (v. 15, viz., at least 2 shekels). ‎ידע‎ והוא לא‎‎ אשר שגג [AND THE PRIEST SHALL MAKE EXPIATION FOR HIM CONCERNING HIS ERROR] WHEREIN HE ERRED AND DISCOVERED IT NOT — Consequently if it came to his knowledge after a time that he has sinned, he is not atoned for by this guilt-offering which he has already bought, but remains unatoned until he brings a sin-offering. To what may this be compared? To the law of the Heifer whose neck was to be broken (as a kind of expiation when it was unknown who has committed the murder) when, on some particular occasion, its neck was actually broken and the murderer was afterwards found — when he surely has to be put to death (Sifra, Vayikra Dibbura d'Chovah, Chapter 21 2).

וְ֠הֵבִ֠יא אַ֣יִל תָּמִ֧ים מִן־הַצֹּ֛אן בְּעֶרְכְּךָ֥ לְאָשָׁ֖ם אֶל־הַכֹּהֵ֑ן וְכִפֶּר֩ עָלָ֨יו הַכֹּהֵ֜ן עַ֣ל שִׁגְגָת֧וֹ אֲשֶׁר־שָׁגָ֛ג וְה֥וּא לֹֽא־יָדַ֖ע וְנִסְלַ֥ח לֽוֹ׃

And he shall bring a ram without blemish out of the flock, according to the valuation, for a guilt offering, to the priest: and the priest shall make atonement for him concerning his ignorance wherein he erred and knew it not, and it shall be forgiven him.