משנה אויף ויקרא 20:16

Cases concerning offenses punishable by death [are decided] by twenty three. A beast that has sexual relations with a woman or with a man is [judged] by twenty three, as it says, “You shall execute the woman and the beast” (Lev. 20:16) and it says, “You shall execute the beast”. The ox that is stoned [is judged] by twenty three, as it says, “The ox shall be stoned and also its owner shall be put to death” (Exodus 21:29), as is the death of the owner, so too is the death of the ox. The wolf, the lion, the bear, the leopard, the panther, or serpent [that have killed a human being] their death is [adjudicated] by twenty three. Rabbi Eliezer says: “Anyone who kills them before they come to court merits.” But Rabbi Akiva says: “Their death must be [adjudicated] by twenty three.