סימן צח סעיף יא
עִסָּה שֶׁלָּשָׁה בְּיוֹם טוֹב מֻתָּר לְהַפְרִישׁ מִמֶּנָּהּ חַלָּה. אֲבָל אָסוּר לְשָׂרְפָהּ, דְּאֵין שׂוֹרְפִין קָדָשִׁים בְּיוֹם טוֹב. וְגַם אָסוּר לֶאֱפוֹתָהּ, מִשּׁוּם דְּאֵינָהּ רְאוּיָה לַאֲכִילָה, שֶׁהֲרֵי כֻּלָּנוּ טְמֵאֵי מֵתִים. וַאֲסוּרָה גַּם בְּטִלְטוּל. רַק בְּעוֹדָהּ בְּיָדוֹ, יַנִּיחֶנָּהּ בְּמָקוֹם הַמִּשְׁתַּמֵּר עַד מוֹצָאֵי יוֹם טוֹב וְיִשְׂרְפֶנָּהּ. וְעִסָּה שָׁלֹשׁ בְּעֶרֶב יוֹם טוֹב, אָסוּר לְהַפְרִישׁ מִמֶּנָּהּ חַלָּה בְּיוֹם טוֹב, אֶלָּא אוֹפֶה וְאוֹכֵל וּמַנִּיחַ קְצָת פַּת שֶׁיַּפְרִישׁ מִמֶּנּוּ בְּמוֹצָאֵי יוֹם טוֹב. וְצָרִיךְ שֶׁיַּנִּיח פַּת כְּדֵי שֶׁיַּפְרִישׁ מִמֶּנּוּ וְיִשָׁאֵר עוֹד קְצָת (עַיֵן לְעֵיל סִימָן ל"ה סָעִיף ט') (תק"ו).
If you knead dough on Yom Tov, you may take challah from it. But you may not burn (the challah portion), because holy things may not be burned on Yom Tov. It is also forbidden to bake (the challah portion)38Shulchan Aruch 506:4. because it is not fit to be eaten, for we are all considered as ritually unclean due to having come in contact with corpses.39Or with people who have been in contact with corpses. (See chapter 202 for details.) And it is forbidden to handle (the challah portion), but while it is still in your hand, you should put it in a safe place until after Yom Tov, and then burn it. If you knead dough on erev Yom Tov, it is forbidden to take challah from it on Yom Tov,40When kneaded before Yom Tov, it is prohibited, rabbinically, because it looks like you are fixing it. When kneaded on Yom Tov, however, they did not prohibit it. (see Mishnah Berurah 506:17) but you may bake (the bread) and eat it, leaving a little bread from which to take (challah)41This is only permitted outside of Eretz Yisrael, where separating challah is a rabbinic ordinance. In Eretz Yisrael, where it is a de’oraisa, you may not eat from it before separating challah. (Mishnah Berurah 506:21) If you want, you may knead a new dough on Yom Tov, put it next to the other dough, and separate the challah of both from the Yom Tov dough, (Rema 506:3) right after Yom Tov. The portion you leave should be sufficient for separating challah and have some left over.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)