Zevachim 155
רבי יהודה אומר אין דם מבטל דם
<br> R. JUDAH SAID: BLOOD CANNOT NULLIFY BLOOD. IF IT WAS MIXED WITH THE BLOOD OF UNFIT [ANIMALS], IT MUST BE POURED OUT INTO THE DUCT. [IF IT WAS MIXED] WITH THE DRAINING BLOOD, IT MUST BE POURED OUT INTO THE DUCT; R. ELIEZER DECLARED IT FIT. IF HE [THE PRIEST] DID NOT ASK BUT SPRINKLED IT, IT IS VALID. <br>
נתערב בדם פסולין ישפך לאמה בדם התמצית ישפך לאמה רבי אליעזר מכשיר אם לא נמלך ונתן כשר:
GEMARA. R. Hiyya b. Abba said in R. Johanan's name: We learnt this only if the water fell into the blood; but if the blood fell into the water, each drop is nullified as it falls. R. Papa observed: [But] it is not so in respect to covering, because there is no rejection in precepts. <br>
<big><strong>גמ׳</strong></big> א"ר חייא בר אבא א"ר יוחנן ל"ש אלא שנפלו מים לתוך דם אבל נפל דם לתוך מים ראשון ראשון בטל
Resh Lakish said: If piggul, nothar and unclean [flesh] were mixed up together, and one ate them, he is not culpable, [for] it is impossible that one kind should not exceed the other and nullify it. You may infer three things from this. You may infer [i]: Interdicts nullify each other. And you may infer [ii]: [The interdict of] taste in a greater quantity is not Scriptural. And you may infer [iii]: A doubtful warning is not called a warning.
אמר רב פפא ולענין כיסוי אינו כן לפי שאין דחוי במצות:
Raba raised an objection: If one made a dough of wheat and rice, if it tastes of corn, it is subject to hallah. Now that is so even if the greater part is rice? - [That is] by Rabbinical law [only]. If so, consider the sequel: A man can fulfil his duty thereby on Passover? <br>