Intro to Halachah/RAB 507 - Class XI Extra Sources - Hilchot Pesach I

...When the 14th of Adar occurs on Sunday one is forbidden to fast on Friday due to the efforts necessary for Shabbat preperation. Since the main agenda of a fast day is the recitation of selichot and extra prayers asking for divine mercy, it will impede properly honoring the Shabbat. The honoring of the Shabbat, which is a Biblical obligation, outweighs the obligation to fast, which is of Rabbinic obligation. Therefore the fast is moved to Thursday, the 12th of Adar.

(5) The morning incense was offered between [offering] the blood and the limbs. The afternoon incense was offered between [offering] the limbs and the wine libations. If the high priest was elderly or squeamish, water would be heated for him and poured into the cold water [in which he would immerse] in order to take the cold edge from it.

(1) On the evening of the fourteenth [of Nissan] we check for chamets [leavened grain products] by candlelight. Any place into which we do not bring chamets does not require checking. And why did [the Sages] say [that we must check up to] two rows in the wine cellar? [It is] a place which we bring leavened bread into. Beit Shammai says, "Two rows upon the entire wine-cellar." But Beit Hillel says, "The two outer rows, which are the uppermost."

(2) We do not need to be concerned [that] perhaps a weasel dragged [chamets] from [one] house to [another] house, or from [one] place to [another] place. Since if [we were to be concerned, we would also need to be concerned that chamets was dragged] from [one] courtyard to [another] courtyard, and from [one] city to [another] city — there [would be] no end to the matter.

And now that it is established that all agree that ‘אור’ means evening, consider: according to both R. Judah and R. Meir, leaven is forbidden from six hours and onward only, then let us search in the sixth [hour]? And should you answer, The zealous are early [to perform] religious duties, then let us search from the morning? For it is written, and in the eighth day the flesh of his foreskin shall be circumcised, and it was taught: The whole day is valid for circumcision, but that the zealous are early [to perform] their religious duties, for it is said, And Abraham rose early in the morning! — Said R. Nahman b. Isaac: [It was fixed] at the hour when people are found at home, while the light of a lamp is good for searching. Abaye observed: Therefore a scholar must not commence his regular session in the evening of the thirteenth breaking into the fourteenth, lest his studies absorb him and he will come to neglect his religious duty.