הלכה על חולין 225:33

To not cook meat in milk: That we not cook animal meat in animal milk, as it is stated (Exodus 23:19), "you shall not cook a kid in its mother's milk." And the explanation came (Chullin 113a) that it is not specifically a kid, but rather all meat of an animal is implied - as the expression, "kid" is an expression that only [applies to] animal meat. And the verse [chose] the expression, "kid," since meat is a soft thing, like a kid. And how is it that you learn like this? From that which you find in several places in the Torah where it is written, "kid," and it was necessary [for the Torah] to explain, "a goat kid." Behold, you have learned [from this] that in a place where is is stated only, "kid," it is not specifically a goat kid, but rather all animal meat like it is implied.

From the laws of the commandment: That which they, may their memory be blessed, said (Chullin 113a), that the prohibition of meat with milk from Torah writ is only with meat of a beast (domesticated animal) that is pure (kosher); but not from an impure beast, not from a [wild] animal - even a pure [one] - and not from a bird, whether pure or impure. And they relied for this upon that which it is written, "kid" three times in the Torah, which is an expression of exclusion, as it should have [otherwise] written, "meat." And the explanation about this came (Chullin 113a), "'A kid' and not an impure beast, 'a kid' and not a [wild] animal, 'a kid' and not a bird." And therefore, they, may their memory be blessed, said that it is permitted to cook these three with milk, and they are permitted in benefit. But they, may their memory be blessed, prohibited them in eating to make a fence for the meat of a beast, which is forbidden by Torah writ, so that people do not switch [one] meat for [another] meat. And hence since the thing is [plausible] that [one] meat will be switched with [another] meat, they were also stringent with this fence, exactly like they were with the meat of beast in some matters, such that they forbade that they be brought up [together] on a table at all. And according to the opinion of some commentators, they obligated about them that there be a pause between their eating and the eating of cheese, like with the main prohibition, which is the meat of a beast. But with the meat of fish and locusts, they did not make a fence with them all, as their meat is not at all similar to the meat of a beast, and people will not come to err in this.