Tractate Shevuot - Chapter 1 - Mishnah 5 שבועות פרק א׳ משנה ה׳

Rabbi Shimon ben Judah said in his name [of Rabbi Shimon (bar Yohai)]: “The new month goats bring atonement for a pure person who ate impure holy food; the festival goats, in addition to bringing atonement for a pure person who ate impure holy food, atone also for a case where there was no knowledge either at the beginning or at the end; the ‘outer’ goat of the Day of Atonement, in addition to bringing atonement for a pure person who ate impure holy food and for a case where there was no knowledge either at the beginning or at the end, atones also for a case where there was no knowledge at the beginning but there was knowledge at the end. They said to him: “Is it permitted to offer up the goat set apart for one day on another?” He said, “Yes.” They [further] said to him: “Granted that the Day of Atonement goat may be offered up on the new month, but how can the new month goat be offered up on the Day of Atonement to bring atonement for a sin that is not within its scope?” He replied: “They are all at least equal [in the wider sense] in that they bring atonement for transgressions of the laws of impurity in connection with the temple and holy food.”