Zevachim 17B

קסבר מחוסר כפורים דזב ⁠– כזב דמי.

The Talmud responds: Rabba holds that a man who experiences a gonorrhea-like discharge [zav] who has not yet brought an atonement offering is still considered to have the impure status of a zav. The impurity of one who has immersed but has not yet brought an atonement offering is therefore considered stronger than that of one who immersed that day but requires no atonement.

ומחוסר כפורים דזב כזב דמי ⁠– תנאי היא; דתניא: שרפה אונן ומחוסר כפורים ⁠– כשרה. יוסף הבבלי אומר: אונן ⁠– כשרה, מחוסר כפורים ⁠– פסולה. מאי, לאו בהא קמיפלגי ⁠– מר סבר: מחוסר כפורים דזב כזב דמי, ומר סבר: לאו כזב דמי?

The Talmud notes: And the matter of whether a zav who has not yet brought an atonement offering is still considered a zav is a dispute between tanna’im, as it is taught in a baraita: If an acute mourner or one who has not yet brought an atonement offering burned the red heifer, it is fit. Yosef the Babylonian says: If an acute mourner burned it, it is fit, but if one who has not yet brought an atonement offering burned it, it is disqualified. What, is it not that they disagree with regard to this: One Sage, Yosef the Babylonian, holds that a zav who has not yet brought an atonement offering is considered a full-fledged zav and therefore disqualifies the red heifer, and one Sage, the first tanna, holds that a zav who has not yet brought an atonement offering is not considered a zav, but is instead considered like one who immersed that day, who is fit to burn the red heifer?

לא, דכולי עלמא ⁠– כזב דמי; והכא בהא קמיפלגי, דכתיב: ״והזה הטהר״⁠ – מכלל שהוא טמא; לימד על טבול יום שכשר בפרה.

The Talmud responds: No, everyone agrees that he is considered a zav, and here the tanna’im disagree with regard to this matter, as it is written with regard to the rite of the red heifer: “And the pure person should sprinkle” the water of purification (Numbers 19:19). The preceding verse already states that the one performing the service must be ritually pure. Therefore, by stating “pure” this verse emphasizes that he needs be pure enough only to perform the rite of the red heifer specifically. By inference, one derives that he may be impure in some way that disqualifies him for other rites. This teaches that one who immersed that day is fit to participate in the rite of the red heifer.