Rabbi Yishmael confronted a puzzle in (Deuteronomy 16:2), which says: "And you shall slaughter the Passover to your God — sheep and cattle." But the Passover offering is supposed to be a lamb. Where do "cattle" come in?
Rabbi Yishmael's solution was elegant. That verse is not talking about the Passover lamb itself at all. It refers to the chagigah — the festive peace-offering that accompanied the Passover sacrifice. The chagigah could indeed come from cattle, while the Passover lamb had to remain exactly that: a lamb.
The proof is in the Torah's own specificity. (Exodus 12:5) explicitly requires "an unblemished lamb, a male" for the Passover offering proper. That verse leaves no room for cattle. So when Deuteronomy mentions "sheep and cattle" in connection with Passover, it must be referring to a different offering brought alongside it.
This reading resolved what might otherwise appear to be a contradiction between two biblical passages. One says the Passover is a lamb; another seems to include cattle. Rather than treating this as an inconsistency, Rabbi Yishmael showed that the two verses address two different sacrifices that happen to occur at the same time. The Passover lamb is one offering with strict species requirements. The chagigah is a separate offering with broader options. Both are part of the Passover festival, but they are legally distinct — and the Torah's precise language keeps them carefully separated.