Gemara

126b (Mishnah): We may clear out even four or five boxes of straw or grain, to make room for guests or Talmidim in the Beis Medrash, but one may not clear out a storehouse;

Question: If we may clear out five boxes, there is no need to say that four are permitted!

Answer #1 (Rav Chisda): We may clear out four out of five boxes [but not everything], or five out of a big storehouse.

Question: What does 'but one may not clear out a storehouse' teach? (The Reisha forbids totally clearing it out!)

Answer: One may not begin to clear out a storehouse [of Muktzeh];

This is like R. Yehudah, who forbids Muktzeh.

Answer #2 (Shmuel): The Tana speaks like people do. He says four or five, but the same applies to more.

'One may not clear out a storehouse' forbids totally clearing it out, lest one even out nooks in the floor.

Inference: 'One may begin to clear out a storehouse' is like R. Shimon, who permits Muktzeh.

141a (Abaye): One may rub his shoe on the ground to clean off mud, but not on a wall.

Objection (Rava): We need not forbid because it looks like building. This is pitiful building! Rather, one may clean his shoe on a wall, but not on the ground, lest he even out holes.

Mar brei d'Ravina: Both of these are forbidden.

Rav Papa: Both of them are permitted.

Question: According to Mar brei d'Ravina, how does one clean his shoe?

Answer: He cleans it on a beam.

124b: Rava was walking in a Reshus ha'Rabim. His shoes got muddy, so he took a piece of Cheres (earthenware) and cleaned them.

Beitzah 35b (Mishnah): One may lower Peros through a skylight on Yom Tov [to save them from rain].

Question: How much is permitted?

Answer (Rav Asi): It is like the Heter to clear out four or five boxes for guests or for a Beis Midrash.

Objection: Perhaps we are more lenient here, lest he lose money!

36a - Question: There, Shmuel explains that one may not finish a storehouse. What is the law here?

Rishonim

Rif (50a) and Rosh (18:1): Some rule like Rav Chisda, for the Sugya and the Stam Mishnah are like him. Some rule like Shmuel, who establishes the Mishnah to be R. Shimon, who permits Muktzeh, and the Halachah follows him

Rosh: The Ba'al ha'Ma'or rules like Rav Chisda, for the Sugya is like him, but he rules like Shmuel's explanation of "but not a storehouse", i.e. one may not finish it. Rav Chisda explained like he did because he forbids Muktzeh, e.g. meat that [spoiled and] swelled [and it is proper only for animals]. The Halachah follows R. Shimon, who permits eating and moving Muktzeh. We can rule like Rav Chisda and Shmuel, for these two matters do not depend on each other.

Rosh: Beitzah 35b connotes that the Halachah follows Rav Chisda regarding four or five, and Shmuel regarding a storehouse. The Rif does not definitively rule like Shmuel or Rav Chisda. The Sugya is like Rav Chisda. However, if we explain the Mishnah like Rav Chisda, "not a storehouse" must refer to beginning it. It cannot discuss finishing, for already the Reisha permits only four out of five! If so, the Stam Mishnah is like R. Yehudah, and the Halachah does not follow him. On 156b, R. Yochanan rules like R. Shimon, and we challenge him from a Stam Mishnah like R. Yehudah [regarding Yom Tov]. In Beitzah 2b, we say that the Stam Mishnah is like R. Shimon regarding Shabbos, and like R. Yehudah regarding Yom Tov. Why didn't we ask from our Mishnah? The Rif brought two Beraisos like R. Yehudah. I do not know why he did.

Rif (58b): Some say that the Halachah follows Mar brei d'Ravina because the Gemara explains his opinion.

Rebuttal (Rosh ibid.): If the Gemara held like him, it would have said 'how does one clean?' Rather, it said 'according to Mar brei d'Ravina...'; because the Gemara disagrees with him!

Rif (ibid.): BaHaG says that the Halachah follows Rav Papa.

Note: The Bach says that the text should say "Rava". It seems that all the Meforshim's text of the Rif said "Rava".

Rebuttal (Ba'al ha'Ma'or): The Halachah follows Rav Papa because he is Basra.

Defense of Rif (Milchamos Hash-m): The Halachah follows Rava against Rav Papa, for Rava was Rav Papa's Rebbi.

Rebuttal #1 of Defense (Rashba 141a DH Ela): Since Rav Papa and Rava did not argue face to face about this, we follow the latter Amora.

Rebuttal #2 of Defense (Gra OC 302:6 DH Mekancho): From Abaye and Rava and onwards we follow the latter Amora even against his Rebbi.

Rambam (Hilchos Shabbos 21:2): One who evens out holes is liable for plowing.

Magid Mishnah: In the field he is liable for plowing. In the house he is liable for building.

Rambam (ibid.): If one must clear out a storehouse for a Mitzvah, e.g. to make room for guests or Talmidim in the Beis Medrash, he may not totally empty it, lest he even out holes. One may scrape his foot against a wall or beam to clean off mud, but he may not use the ground, lest he even out holes. One may not spit on the ground and rub it with his foot lest he even out holes. One may 'innocently' step on spit while walking.

Poskim

Shulchan Aruch (OC 302:6): If there is mud on one's foot (Rema - or shoe), he may scrape it against a wall to clean it, but he may not use the ground, lest he even out holes.

Magen Avraham (10, citing Magid Mishnah): We are concerned lest he forget and intentionally even out holes in the ground. If not, it would be Davar she'Eino Miskaven, which is permitted.

Beis Yosef (DH Tit): Mahari Avuhav leans to forbid if the dirt is on his shoe, for the Gemara (141b) forbids scraping both new and old shoes.

Beis Yosef (ibid.): There is different, for a fingernail or the back of a knife is Memachek (smoothing, a Melachah). Cleaning on the wall or ground is not Memachek. Even if it is Memachek, it is Davar she'Eino Miskaven.

Rebuttal (Bach DH v'Ika): Mahari Avuhav is unsure whether one may scrape firmly. We cannot learn from Rava, who gently cleaned his shoe. The Cheres did not touch the shoe. If Rava permits due to Davar she'Eino Miskaven, he should permit also on the ground! The Rema was swayed by the Beis Yosef, and permits even shoes. However, in the Shulchan Aruch, the Beis Yosef himself was stringent like Mahari Avuhav, and permits only to clean one's foot! We should not rely on the Rema. The Rif says that some are stringent like Mar bar d'Ravina. We permit only when one's feet are muddy, for then he feels pain.

Mishnah Berurah (26): One may clean shoes against a step. In any case it is permitted if one scrapes gently, especially if the mud is wet.

Kaf ha'Chayim (42,45): It is best to be stringent about shoes unless they are so muddy that it is painful to walk, or for a Mitzvah such as going to a Beis ha'Keneses.

Shulchan Aruch (ibid.): Some forbid even against a wall.

Mishnah Berurah (27): This applies to a stone wall. It looks like he adds onto the wall and strengthens it. It is permitted against a single rock, or against a wall of wood, for it is just like a beam.

Kaf ha'Chayim (44): A wooden wall plastered with mud is forbidden. Or, perhaps it is permitted, for Chazal did not decree about this in their time.

Rema: Some permit to use either.

Mishnah Berurah (28): Even this opinion forbids intentionally cleaning where there is a hole in the ground, for he intends to fill it. The Taz follows this lenient opinion, for it is a mid'Rabanan matter; others are stringent. Certainly one may be lenient to use a wall, for most Rishonim permit it.

Shulchan Aruch (333:1): One may take barrels of wine from a storehouse in order to drink, but he may not begin to clear it out, unless it is for a Mitzvah, e.g. to make room for guests or for a Beis Medrash. One may clear out five boxes [of three Sa'im each]. If it contained only five boxes, one may clear out four, but not all, lest the even out holes.

Beis Yosef (DH Mi): The Rosh, Rambam, Ramban and Rashba hold like the Ba'al ha'Ma'or. The Rosh asked why the Rif brought the Beraisos like R. Yehudah. The Rambam taught that the Isur to begin a storehouse is not due to Muktzeh. Rather, it is when he does not take to eat. He merely wants to clear it out. We permit only for a Mitzvah.