משנה אויף ויקרא 5:16

Five things in an olah combine with one another: the flesh, the fat, the fine flour, the wine and the oil. And six in a todah: the flesh, the fat, the fine flour, the wine, the oil and the bread. Terumah, terumah of the tithe, terumah of the tithe separated from demai, hallah and first-fruits combine with one another to make up the size required to render other things forbidden and to be liable for the payment of a fifth.

Rabbi Akiva declares one liable to an asham talui for sacrilege; But the sages declare him exempt. Rabbi Akiba admits that he does not bring his restitution money until he becomes aware [of his trespass], when he must bring with it a certain asham. Rabbi Tarfon: Why should he bring two ashams? Rather, let him set aside the principal with an added fifth, and bring an asham the value of two sela's and stipulate: “If I did commit sacrilege, here is my restitution and this my asham; and if the sacrilege was doubtful, let the money be a freewill gift and the [offering an] asham talui;” since the same type of sacrifice he brings for a case where he doesn’t know, he brings for one where he does know.