Rashi on Leviticus 5:18/רש"י על ויקרא ה׳:י״ח

1‎ 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).

2‎ידע‎ 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).