Rif Pesachim 3a {Pesachim 6a continues ... 7a}

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3a

{Pesachim 6a continues}
before Pesach 30 days.
What is the reason? {Pesachim 6b} For Moshe stood on Pesach Rishon {=Pesach} and gave instructions regarding Pesach Sheni {for those who were impure, and Pesach Sheni was 30 days later}.

Rav Yehuda said {our gemara: Rav Yehuda cited Rav}: One who searches {for chametz} needs to nullify it.
How should he nullify? He says as follows: (All chamira {=leaven} which is in my domain which I have not seen and have not destroyed should be nullified and reckoned like dust.)

{Bach brings a different version: All chamira {=leaven} which is in my domain which I do not know about should be nullifed and reckoned like the dust of the earth.)

What is the reason {for this nullification}? Rava said: As a decree lest he find a tasty loaf and set his mind upon it {to keep it until after Pesach}.
And let him nullify it when he finds it! He may find it after it is already prohibited and will not be able to nullify it, because it is not in his domain. For Rabbi Eleazar cited Rabbi Yishmael: Two things are not in a man's domain and Scripture makes them as if they are in his domain: a pit {bor} in the public domain and chametz from 6 hours and on.
And let him nullify it in the 6th {hour}?!
{Pesachim 7a}
Since there is a Rabbinic prohibition upon it, he cannot nullify it, for it is not in his domain. For Rav Gidel cited Rav {our gemara: Rav Gidel cited R' Chiyya bar Yosef who cited Rav}: One who betrothes a woman with chametz from 6 hours and on, even with wheat of Cordyene, which is hard and dry {and thus does not easily become chametz, yet water fell on it after harvesting and so it is reckoned as chametz}, we have no fear of his betrothal {to consider the woman married}, for their {the chametz} benefit is prohibited.

And let him nullify it in the fourth or fifth hour?