Beitzah 8B

והא מדקתני סיפא: ואם שחטו ⁠— אין מכסין את דמו, מכלל (דרישא) בדאית ליה עסקינן!

The Talmud challenges this: From the fact that the latter clause teaches: And if he slaughtered it one may not cover its blood, it may be inferred that in the first clause we are dealing with a situation where he does have something with which to cover the blood. If he does not have anything he can use, why is it necessary to state that one may not cover it? And consequently, if he does in fact have material with which to cover the blood, why may he not do so, either with his basket of earth, in accordance with the opinion of R' Yehuda, or with the ashes of a stove?

אלא אמר רבה: אפר כירה ⁠— מוכן לודאי ואין מוכן לספק.

Rather, Rabba said that the ashes of a stove, which the Mishnah stated are prepared, are prepared only for covering the blood in a case of a definite obligation, but they are not considered prepared for a case of uncertainty. Although his intention was to use these ashes to cover the blood of any animal he slaughters, whether in a definite or an uncertain case, they are nevertheless not considered prepared for an uncertain case.

לספק מאי טעמא לא ⁠— דקא עביד גומא, ודאי נמי קא עביד גומא! אלא כדרבי אבא, הכא נמי כדרבי אבא!

The Talmud inquires: In a case of uncertainty, what is the reason that the ashes are not considered prepared? If the reason is that one makes a hole in the mound of ashes when he removes part of it for covering, in a definite case he also makes a hole. If it is prohibited to make a hole, that prohibition applies in all cases. Rather, one must say, in accordance with the opinion of R' Abba, that the making of this hole is not considered prohibited labor, as he is merely performing a destructive act. If so, here too, in a case of uncertainty, there should be no cause for concern, in accordance with the opinion of R' Abba.