Sefer HaChinuch ספר החינוך

The commandment of the sacrifice of an undetermined guilt-offering: That one who is in doubt if he sinned one of the big sins for which a man is liable excision when he does it volitionally and a fixed sin-offering when inadvertent, bring a sacrifice (Keritot 25a). And the doubt emerges for him in this way: As you might say, by way of an archetype, that there were two pieces in front of him — one of forbidden fat and one of permissible fat — and he ate one of them and the other got lost. And [so] he worries to himself as he does not know if he ate the one of forbidden fat or the one of permissible fat. This sacrifice that is brought upon this doubt is called an undetermined guilt-offering. And the word undetermined (talui) is said about anything about which it is fitting that a matter come afterwards that reveals about it that which was not known previously. For example, if [one] knows that the sinner ate forbidden fat — behold, it is revealed that the first [sacrifice] was not sufficient for him and he needs to still bring another sacrifice that is called a fixed sin-offering to complete his atonement; but if one knows about him that he ate what was permissible — behold it is revealed that the first was sufficient and he does not need to bring another sacrifice after it. This is the explanation of its being undetermined. And the command for this sacrifice is from that which it is written (Leviticus 5:17-18), “And if a soul sins and does one of all of the commandments of the Lord which you shall not do and he does not know, but he is guilty and he shall bear his iniquity. And he shall bring an unblemished ram from the flock, according to your assessment for a guilt-offering to the priest, and the priest shall atone for his inadvertent transgression which he transgressed and did not know” — meaning to say, about his not knowing if he transgressed inadvertently or [not]. And the Sages called this matter, “not known.”

It is from the roots of the commandment that a man should be careful, fear sin and analyze his deeds with a proper analysis that he not stumble in the matter of a sin. And hence the Torah required him to bring a sacrifice when he was not careful [enough] in his deeds to the point that this doubt would not have come up. And the proof that this only comes to atone for his laziness is that behold it does not uproot [it for] him, to atone for the sin at all. [Rather,] when the sin is made known to him, he immediately needs a complete sacrifice; [just] as he would have been liable if he had not offered the first one.

From the laws of the commandment is that which they, may their memory be blessed, said (Keritot 18a) that there is never a liability for this sacrifice until there is an established prohibition there. For example, that there be two pieces in front of him and one of them is certainly forbidden fat — as behold there is an established prohibition here, and he ate one of them. And so [too,] if he ate a certain forbidden fat, but he is in doubt if there was a whole kazayit or not (Keritot 17a) — this too is an established prohibition. But if there was one [piece] in front of him and it is a doubt if it was forbidden fat or permitted fat, and he ate it — he is exempted from the sacrifice, as there is no established prohibition here; for perhaps there is no prohibition here at all. And from this reason they said that one who has sexual relations with a woman the divorce of which is in doubt is liable for a sacrifice; for behold, there is an established prohibition here, such that we evaluate her according to [that which is] established about her. But one who has sexual relations with a woman the marriage of which is in doubt is exempted from a sacrifice, as there is no established prohibition here; and behold it is like one piece with a doubt if it is forbidden fat or permitted fat, such that he is exempted from a sacrifice (Ketuvot 22b), as we have said. And the rest of its details are elucidated in Keritot. (See Mishneh Torah, Laws of Offerings for Unintentional Transgressions 8.)

And [it] is practiced at the time of the [Temple] by males and females. And one who transgresses it and does not offer this sacrifice if a doubt happens to him that makes him liable for it has violated a positive commandment.