The 187th prohibition is that we are forbidden from eating a mixture of meat and milk.

The source of this prohibition is G‑d's statement,1 "Do not cook meat in its mother's milk," which is repeated in order to prohibit its consumption.

Our Sages said in tractate Chulin,2 "A mixture of meat and milk — one is lashed for cooking it and one is lashed for eating it." And in tractate Makos3 they said, "One who cooks a sciatic nerve in milk on a holiday and eats it receives five sets of lashes: for eating the sciatic nerve, for cooking the sciatic nerve, for cooking a mixture of meat and milk, for eating a mixture of meat and milk, and for making a fire." There they also say, "Delete 'making a fire' and add '[burning] sanctified wood,' which is prohibited by the verse,4 "Burn their Asherah trees...Do not do this to G‑d your L‑rd."

Our5 Sages said in tractate Chulin,6 "The Torah expressed the prohibition against eating [meat and milk] with the word 'cook' in order to teach that just as one is lashed for cooking, one is lashed for eating." And they said the following about meat and milk in the second chapter of Pesachim:7 "The Torah did not explicitly write the prohibition of eating in order to teach that one is lashed even if it was eaten without enjoyment."8 Remember this.

This is the appropriate place to point out an important idea which has not yet mentioned — that G‑d's statement, "Do not cook meat in its mother's milk," is repeated in the Torah three times.9 Those who passed down the Oral Tradition say that each prohibition has a different implication. They explained,10 "One is to prohibit eating, one to prohibit having benefit, and one to prohibit cooking."

Someone could possibly challenge me as follows: Why did you count eating and cooking as two separate mitzvos and not count having benefit as a third mitzvah? The questioner must know that having benefit cannot be counted as a separate mitzvah since it and eating are the same idea, since eating is just one type of benefit. G‑d's statement that a certain thing may not be eaten is just giving one example of benefit, meaning that one may not have any benefit, not by eating it or in any other way. This is seen from the statement of our Sages,11 "Everywhere it says, "lo socheil" or "lo soch'lu" ("Do not eat"), both eating and other forms of benefit are prohibited, until the Torah specifically states [that one may have other types of benefit] as it did with neveilah." In that case the Torah says that benefit is allowed, as seen from G‑d's statement,12 "You may give it to the resident alien in your settlements so that he can eat it, or you may sell it to a non-Jew."

According to this principle, eating and having other forms of benefit cannot be counted as two separate mitzvos. And if we counted them as separate mitzvos in the case of meat and milk, we would also have to do so in the cases of chometz, orlah, and kilai hakerem, with all four mitzvos having separate prohibitions for other types of benefit. In these cases having benefit is not counted and only the prohibition of eating is counting, with benefit being included, in accordance with the principle we explained — the same applies in the case of meat and milk.

Only one last question could be asked: Since — as our Sages (may they rest in peace) said — the prohibition of having benefit is self-understood from that of eating, why was it necessary to write a third prohibition to prohibit having benefit, as we explained above?

The answer is based on the fact that for meat and milk the Torah does not actually use the expression "Do not eat," which would have prohibited both eating and other forms of benefit. A separate statement was therefore necessary in order to prohibit having benefit. And we already mentioned the reason why the Torah didn't mention "eating" meat and milk — because anytime "eating" is prohibited, one is guilty only if he benefits from the eating. But if he opened his mouth and swallowed something prohibited [without tasting it], or ate it when it was so hot that it burned his throat and caused him pain when he swallowed it, etc. — then he is exempt [from punishment]. but meat and milk is an exception, and he is culpable for eating it even if he derived no benefit, as mentioned by our Sages.13 The same applies to kilai hakerem, as we will explain later.14 Understand all these principles and remember them.

The details of this mitzvah are explained in the 8th chapter of tractate Chulin.