On a festival, we are permitted to cook only the food that will be eaten on that festival itself. It is even forbidden to cook for the second day of the festival on the first day. When a festival falls on Thursday and Friday, a problem may thus ensue, for it is forbidden to cook on the Sabbath. To allow for food to be cooked for the Sabbath in such an instance, our Sages established the practice of setting aside an eruv tavshilin. Every person should establish such an eruv for his household and do so in a manner in which the option is granted to others to rely on this eruv as well.

The following procedure should be carried out. A person should take matzah prepared for the Shabbos as well as a highly regarded cooked food, e.g., meat or fish. He should hand the matzah and the cooked food to another person who is not a member of his household and say:

I hereby grant a share in this eruv to anyone who wishes to participate in it, and rely on it.

The person to whom the matzah and the cooked food was given raises them a handbreadth and then returns them to the person making the eruv. That person then says

Blessed are You, G-d, our L-rd, King of the universe, who has sanctified us with His commandments and commanded us concerning the mitzvah of eruv.

Through this, it shall be permissible for us to bake, to cook, to cover [a dish and insulate it so that its heat will not dissipate], to kindle a light, and prepare and do on the festival all that is necessary for the Sabbath. [This dispensation is granted] for us and for all Israelites who dwell in this city.