Zevachim 98B

דם חטאת למטה ודם עולה למעלה, טעון כיבוס.

when the blood of a sin offering is below and the blood of a burnt offering is above, in a case in which the blood of a burnt offering is sprayed as a second layer on top of the blood of a sin offering that has already been sprayed and absorbed into a garment, the garment requires laundering.

בעי רבא: דם עולה למטה ודם חטאת למעלה, מהו? משום נוגע הוא ⁠– והא נוגע; או דלמא משום בלוע הוא ⁠– והא לא בלע (הוא)? הדר פשטה, דאין טעונין כיבוס.

Rava asks: When the blood of a burnt offering is below and the blood of a sin offering is above, what is the halakha? Is one required to launder a garment to remove the blood of a sin offering because the blood touches his garment, and in this case, this blood is touching the garment? Or perhaps is one required to launder it because of the absorption of the blood into the garment, and, in this case, since the garment has already absorbed the other blood, this garment did not absorb the blood? Rava then resolves his dilemma, ruling that such garments do not require laundering.

אמר רבא: פשיטא לי, דם על בגדו ⁠– חוצץ, ואם טבח הוא ⁠– אינו חוצץ. רבב על בגדו ⁠– חוצץ, ואם מוכר רבב הוא ⁠– אינו חוצץ. בעי רבא: דם ורבב על בגדו, מהו?

§ In a similar manner, with regard to the immersion of a garment that has become impure, Rava said: It is obvious to me that if there is blood on one’s garment, it interposes between the water of immersion and the garment, such that the immersion is ineffective. But if he is a butcher, used to having blood on his garments, a bloodstain does not interpose, and the immersion is effective, since a substance is not considered an interposition if the one immersing is not particular about it. Similarly, if there is a stain of fat [revav] on one’s garment, it interposes. But if he is a fat seller, such a stain does not interpose. Rava asks: If there is both blood and fat on one’s garment when he immerses it, what is the halakha?