Deuteronomy 26:14 "Neither have I consumed any part of it while impure"

This Negative Mitzvah applies to the manner of eating Ma'aser Sheini. (See Introduction to Negative Mitzvot 141-144.)

This is a portion of our harvest, set aside to be brought up to Jerusalem and eaten there. This Negative Mitzvah prohibits one who is impure from eating the Ma'aser Sheini.