Mishnah Berurah — משנה ברורה

Offered voluntarily - But after [reciting] the passage of the sin-offering, he should not say it, since it is not brought voluntarily; unless he transgressed a sin that obligates him to bring a sin-offering. And so too [regarding] the guilt-offering. [Regarding] an uncertain guilt-offering, we maintain that it is not offered voluntarily. The later rabbinic authorities wrote in the name of Rasha"l, that one should say the "Yehi Ratzon" even after [reciting the passages of] the sin and guilt offerings, but he should say it using words that convey an uncertainty, such as: "May it be Your will, that if I transgressed a sin that requires a sin-offering, that it (ie. my reading of the passages) should be considered as if I offered a sin-offering"; and if not, it should be like I just read from the Torah. And one should say [a "Yehi Ratzon"] in a similar fashion after reciting the passage of the guilt-offering. However, the Magen Avraham had great difficulty with this - how can one say "if I became obligated in a sin-offering"? Behold, we maintain regarding a sin-offering that it requires one to have knowledge [of the sin] before he sins!(So how could he say "if"??) Therefore, the Magen Avraham concludes that regarding the sin-offering, one should not say the "Yehi Ratzon" at all; but for the certain guilt-offering and the uncertain guilt-offering, one may say this conditional "Yehi Ratzon". But if one's heart is beating (ie. he is nervous), that perhaps he transgressed a sin, and he had knowledge of the sin, but then he forgot, he may say the conditional "Yehi Ratzon" after the guilt-offering [passage]. [Shaarei Teshuva].