Tosefta su Levitico 17:78

[The requirement to] cover the blood [of a wild animal or fowl] (Lev. 17:13) applies to mixed-breeds and to the k'vi. Rabbi Eliezer says, this applies to mixed-breeds from a goat and from a ewe. It does not apply [to mixed-breeds] from a k'vi. Rabbi Yosei says, we may not slaughter it (i.e., a mixed-breed from a k'vi) on a Festival because of the doubt [as to whether or not it is a wild animal], but if it was slaughtered, we do not cover the blood. Said Rabbi Yosei, and what about circumcision, which is a definite obligation that overrides the Sabbath, but when it is a doubtful obligation it does not override a Festival, [thus] covering the blood [of a mixed-breed from a k'vi], that even when it is a definite obligation it does not override the Sabbath, is it not logical that where it is a doubtful obligation it would not override a Festival? They said to him, [the blowing of] trumpets [on Rosh Hashanah] in the outlying areas will prove it. That they are ("שכן ודאה" not "שאין ודאן") definite obligations and they do override the Sabbath, and [even] when they are doubtful obligations (i.e., if it is unknown whether today or tomorrow is Rosh Hashanah), they [nonetheless] override a Festival, they prove that as to covering the blood, that even though it is not a definite obligation (i.e., one is only required to cover the blood in the event that one happens to slaughter), it overrides the Sabbath, would it not follow that when it is only a doubtful [obligation] (i.e., involving a k'vi), it [would nonetheless] override a Festival? Rabbi Elazar (=Bar Kappara) the son of Rabbi Elazar HaKappar responded, "And what [is noteworthy] about circumcision is that when it is an uncertain [obligation] it does not override a Festival, and when it is a certain obligation it does not override Festival nights (i.e., it cannot be performed at night). You must [therefore] say that with respect to covering the blood, that when it is a certain [obligation] it overrides Festival nights, since [all] certain [obligations] override Festival nights, it is logical that [even] if there is a doubt, it would override a Festival." Said Rabbi Abba, this is one of the things that Rabbi Achiyya (alt. "Rabbi Chiyya," =רבי חייא, see Hul. 84b:9) would say, "There is no refutation to this," and Rabbi Chiyya (alt. Rabbi Elazar HaKappar" =רבי אלעזר הקפר, ibid) refuted it.