[If] the fourteenth [of Nissan] falls on the Sabbath, we remove everything before the Sabbath —- [these are] the words of R' Meir.  But the Sages say: [Everything is removed] at its [usual] time;  R' Elazer bar Tzadok says: Terumah [must be removed] before the Sabbath and chullin at its [usual] time.

[If] someone is going to slaughter his pesach-offering, to circumcise his son, or to dine at a betrothal feast at the house of his father-in-law, and he remembers that he has chametz at home —- if he is able to return, remove [it], and [then] return to his mitzvah, he must go back and remove [it]; but if not, he nullifies it in his heart.  [If he is on his way] to save [people] from a [marauding] troop, from a river, from bandits, from a fire, or from a collapsed building, he nullifies it in his heart. [If] it was but to establish a voluntary resting place, he must return at once.