Rambam - Sefer HaMitzvos: Negative Mitzvot 217, 218: Negative Mitzvot 217, 218

Negative Mitzvah 217: It is forbidden to breed two types of animals together
Leviticus 19:19 "You shall not let your cattle breed with a different kind"

We ae not allowed to breed one type of animal with another animal of a different species. This is also known as Kelayim.

Negative Mitzvah 218: It is fobidden to work with two different kinds of animals together
Deuteronomy 22:10 "You shall not plow with an ox and donkey together"

This is another type of "forbidden mixture" or Kelayim, concerning animals.

We are not allowed to do any work while harnessing two different kinds of animals together.

You must always have good things to think about. An empty mind is a vacuum awaiting destructive thoughts.

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Where your thoughts are -- that is where you are, all of you. Try to be always in good places.

From: Bringing Heaven Down to Earth by Tzvi Freeman - tzvif@aol.com