Pesachim 3:6

Rabbi Meir says that if 14 Nisan falls on Shabbos, chometz is removed before Shabbos. The Sages say it is removed at the usual time (i.e., on Shabbos). Rabbi Eliezer ben Tzadok says that terumah must be removed before Shabbos but that other chometz is removed at the usual time.

Pesachim 3:7

If, on 14 Nisan, a person was on his way to offer his Passover sacrifice, to circumcise his son, or to eat an engagement meal at his father-in-law’s house, and he remembers that he has chometz at home, then if he is able to return home, dispose of his chometz, and resume his mitzvah, he must do so. If this is not possible, he nullifies it mentally (i.e., he considers it worthless, like dust). If he is on his way to save people from enemy soldiers, a river, bandits, fire or a collapsed building, he nullifies it mentally. If he is on his way to place an eiruv techumin (to shift his Shabbos boundary), he must go home immediately in order to deal with the chometz in person.