הלכה על ביצה 6:12

We hold that a safek isur Torah is asur, and the opinion of the Rambam in his great work [Mishneh Torah] in several places, is that this rule is only mid'rabanan, and that mid'oraisa all case of doubt are mutar. This is also the opinion of the Raavad. But the Ramban and the Rashba argue and they prove that when Chazal say "you must be stringent on a doubt of Torah prohibiton", that is mid'oraisa. And the Pri Chadash in Yoreh Deah elaborates on this. See there, section 110.

And that which we said that a creature is not neutralized and the intention was to say whether alive or dead - [that is] specifically a creature that is forbidden from the beginning of its creation, such as an impure beast or an impure swarming creature; and so [too,] a sciatic nerve, as it too is forbidden from the beginning of its creation. But a beast that is fit (kosher) from its beginning is only not neutralized when it is still alive - on account of living animals being significant and [so,] not neutralized (Zevachim 73a). But after it dies, it certainly [can have] neutralization; and we say that it [can be] neutralized, even with a large dead ox. And this is according to Rabbi Yochanan - as the law follows him - who said in the Gemara (Beitzah 3b) regarding significant things that are not neutralized, "We learned things that it is their way to be counted." [This is] meaning to say that we learned that the things that are not neutralized are those that it is the way of people to always count due to their importance, such as the seven designated above. But it is not the way of people to always consider an ox significant in their hearts; since it is not fit at the time, and [so] its benefit is not close to the hearts of people like those seven things.

And I have already written some of the differences of the places surrounding the Land of Israel concerning the seventh [year] in the Order of Eem Kesef Talveh. And I will still write at length [about] the whole matter of priestly tithes and [other] tithes and the distinctions of the places and that which is from Torah writ and what is rabbinic in the Order of Shoftim in the commandment of the separation of the great priestly tithe (Sefer HaChinukh 507) - take it from there. And I will also inform you there of a disagreement among the commentators regarding whether the priestly tithe is from Torah writ or rabbinic today even in the Land. And [regarding] one who is in a place about which he is in doubt if it is from the Land of Israel or not, at the time when the land is in its inhabitation - it is fitting for him to be stringent nonetheless, since it is prohibition from Torah writ; and it is established for us that [in the case of] a doubt in Torah law, [we go] towards stringency (Beitzah 3b). And from that which it appears, the Sages, may their memory be blessed, were stringent (Chullin 6b) in the places about which they were in doubt if they were from the Land of Israel, even about the fruits the tithing obligation of which was only rabbinic - even after the destruction of the Temple, even though this prohibition is only practiced [altogether] from Torah writ [when the Temple is standing]. And one who transgresses this and ate a kazayit of tevel before they separated the great priestly tithe from it - and likewise before they separated the priestly tithe of the tithe - is liable for death by the hands of the Heavens, and as we said above. But if he ate a kazayit of tevel from which the great priestly tithe and the priestly tithe of the tithe were taken, but they still did not separate the tithes from it - and even if only the poor tithe remained in it - he is liable for lashes. And if it was tevel from their words - meaning something that the obligation of priestly tithes and [other] tithes from which is only rabbinic, such as all the fruits besides grain, wine and [olive] oil of the Land of Israel and at the time of the Temple - we strike him with lashes of rebellion. And the liquids that come out of the fruits that are tevel are forbidden like them. And nonetheless even though they are are forbidden from Torah writ, the liability for lashes is not on the liquids but only only on the body of the fruits - except for wine and [olive] oil, such that we administer lashes for them in the same way that we administer lashes for the olives and grapes [themselves]. And the reason, according to that which appears, is because the essence of those fruits for the creatures is for [their] liquids.

And behold it is seen that our Rabbis in all of the Gemara say the opposite of this. As behold, they determine all rabbinic cases leniently, as they always say (Beitzah 3b), "A doubt of Torah [law] is to be [ruled] stringent and a doubt of rabbinic [law] is to be [ruled] lenient. And they were lenient regarding a concern of rabbinically forbidden [products being present in a certain food], to say, "As I say" (that we can assume that it is not present). And they said in the first chapter of Pesachim 9b, "I will say that we say, 'As I say,' in a rabbinic [law]; in a Torah [law], can we say, 'As I say?'" And they relied upon minors who are not fit to testify, to testify on that which is rabbinic, as they said (Pesachim 4b), "The checking for chamets is rabbinic, and the Rabbis relied upon them in rabbinic [laws]." And so [too,] regarding perimeters, a minor is believed to say, "The perimeter of Shabbat is to here," [as they] "held that perimeters are rabbinic, and the Rabbis were lenient in the rabbinic," as it is found in Eruvin 58b and in Ketuvot 28b. And they were also likewise lenient in the rabbinic with doubts, as they, may their memory be blessed, said (Berakhot 21a), "[If] there is a doubt if he prayed or if he did not pray, he does not go back and pray; [if] there is a doubt if he said, 'True and solid' or he did not say it, he goes back" - and they said, "What is the reason? Prayer is rabbinic; 'True and solid' is from the Torah." And not only that, but they were even lenient about things that contradict each other in rabbinic [law] - as they said in the chapter [entitled] Bemeh Madlikin (Shabbat 34a), "[If] two [people] said to him, 'Go out and make an eruv for us'; he made an eruv for one while it was still day, etc.," as it appears there. And it is also seen in the Gemara that we constantly uproot their words on account of a Torah prohibition; as they said in Tractate Shabbat 4a, "If he stuck bread onto an oven [wall], they permitted him to scrape it off before he comes to a prohibition [that is punished with] stoning." And there in Shabbat 128b they said, "Negating a vessel from its preparedness is rabbinic, but the pain of animals is [from] the Torah, and a positive commandment [from] the Torah comes and negates a positive commandment [from] the Rabbis," as it appears there. And this is [something seen] very much in the Talmud - a positive commandment [from] the Torah comes and pushes off a positive commandment [from] the Rabbis. And so [too] with a disagreement among the Sages, they said (Avodah Zarah 7a), "If one [group] was greater in wisdom, follow it; and if not, follow the stringent [one] in that of the Torah, and the lenient in that of the [Rabbis]." And even greater than this, they said (Eruvin 67b), "In that of the [Rabbis,] we first do the act, and then we deliberate." And in the chapter [entitled], Mi Shehichshikh (Shabbat 154b), they said, "What is it that you would say? They were also concerned with a small loss. Hence, it makes us hear" - as it is a novelty with them when they do not push off the words of the [Rabbis], even for a small loss. And they said (Berakhot 19b) that priests can render themselves impure with rabbinic impurity to see kings of the nations of the world; so that if they merit [it], they will differentiate that [which separates] the kings of Israel, etc. And also regarding the punishments of the words of the [Rabbis], they only have excommunication, as they said (Pesachim 52), "We excommunicate for the two days of holiday in the Diaspora." And they said about one who does work on Purim, "Let the master excommunicate him." And in [some] places, they have lashes of rebellion, and that is for one that transgress their words that are similar to [commandments] of the Torah - and those are all the decrees that they decreed from their [own] words - that they lash him until he accepts it upon him or until his soul departs, as is explained in the Tosefta of Sanhedrin. The general rule of the matter is that the words of the [Rabbis] are different in all of their laws from the words of the Torah, that [the one tends] towards leniency, and [the other] towards stringency. But the thing that is clear and clean of any confusion is that this negative commandment of "you shall not stray" is only in that which they, may their memory be blessed, said in explanation of the Torah - such as things that are expounded through a gezerah shavah or a binyan av or the rest of the thirteen methods through which the Torah is expounded; or about the meaning of the language of the verse itself - and so [too] regarding that which they received as a law of Moshe from Sinai. And it is about this that they, may their memory be blessed, said that there is a positive commandment and a negative commandment in the thing. And if in this matter, one fitting to pronounce decisions disagrees with the Great Court about that which the volitional transgression [brings] excision and the inadvertent violation [brings] a sin-offering, he becomes a rebellious elder through them - at a time when we judge capital cases. And this is [the meaning of] that which they, may their memory be blessed, said (Sifrei Devarim 154), "Even if they tell you about the left that it is right"; meaning to say that this is the commandment upon us from the Master of the Torah, may He be blessed - that we believe the greats regarding what they say, and that the one who disagrees not say, "How can I permit it for myself, since I know with certainty that they are mistaken?" As even if it will be such, it is a commandment to listen to them - as I wrote above at the beginning of the commandment - and like the matter that Rabban Gamliel conducted with Rabbi Yehoshua on Yom Kippur that fell out according to [the latter's] calculation, as is mentioned in Rosh Hashanah 25a.