Zevachim 40B

אמין שבאצבע. ״בדם״⁠ – שיהא בדם שיעור טבילה מעיקרא. ״וטבל״⁠ – ולא מספג.

service performed by a priest who has a wart or blister on his finger. These are not considered an interposition between his finger and the blood. With regard to the term “in the blood” (Leviticus 4:6), this teaches that the blood in the service vessel must be of a sufficient measure for immersion from the outset. The priest must initially collect in the vessel enough blood for all the sprinklings, rather than adding blood to the vessel for each sprinkling. Finally, the term “and the priest should immerse his finger in the blood” indicates that there must be enough blood in the vessel such that the priest can immerse his finger in it and not have to wipe the sides of the utensil to collect blood for sprinkling.

ואיצטריך למכתב ״בדם״, דאי כתב רחמנא ״וטבל״⁠ – הוה אמינא: אף על גב דליכא שיעור טבילה מעיקרא; כתב רחמנא ״בדם״.

The Talmud explains: And it was necessary for the verse to state both these last two terms. It had to write “in the blood,” as had God written only “and the priest should immerse,” I would say that the sprinklings are valid even if there was not a sufficient measure of blood for immersion from the outset, but only enough for a single sprinkling, provided that the priest then added more blood to the vessel for each sprinkling. Therefore, God writes “in the blood” to teach that from the outset there must be enough blood in the vessel for all the sprinklings.

ואי כתב רחמנא ״בדם״⁠ – הוה אמינא: אפילו מספג; כתב רחמנא: ״וטבל״.

And conversely, had God written only “in the blood,” I would say that even if there was enough blood in the vessel at the outset it is not necessary that there be enough blood for immersion for the last sprinklings, as the priest can wipe the sides of the utensil to collect blood for sprinkling. Therefore, God writes “and the priest should immerse.”