[If] one makes a dough from wheat and rice, if it has the taste of grain, it is obligated in challah, and one can discharge his obligation on Pesach with it. But if it does not have the taste of grain, it is not obligated in challah, and one cannot discharge his obligation on Pesach with it.

[If] one takes sourdough from a dough whose challah has not been separated and places [it] into a dough whose challah has been separated, if he has a supply from elsewhere, he may separate [challah] proportionally; but if not, he must take one challah for the whole [dough].