Rabbi Shmuel haNagid (993-1056 CE)'s intro. to the Talmud, as included in the 'Aiding Talmud Study' by Aryeh Carmell, from Feldheim Publishers:
Aggada [Aramaic: agadata]: everything mentioned in the Gemara [Talmud], which is not directly connected with the halakhic aspect of the commandment. One should learn from such statements ONLY those things which our minds can grasp. It is important to know that ALL MATTERS which our Sages established as LAW, in connection with the commandment transmitted by Moshe Rabbenu [Moses our teacher] who received it from the Almighty CANNOT be augmented or diminished in any way (see Deuteronomy 17:8-11)...
HOWEVER, the [aggadic] explanations they rendered of biblical verses were in accordance with their INDIVIDUAL VIEWS and the ideas WHICH OCCURRED to them. We should learn from them insofar as our minds can grasp them, but otherwise we SHOULD NOT build upon them.""
Rambam's 'Commentary to the Mishna' to Seder Nashim in Sanhedrin chapter 10 (pereq Hheleq) on page qof-mem-heh of Rabbi Yosef Qafehh's translation from the Arabic original:
""[gimal] We have already mentioned to you a number of times that all disagreements that are between Sages [hhakhamim] and that aren't (things) that are with regard to [that hang on] actions, (but) rather establish an opinion alone, there is no place to arrive at a legal conclusion / decision [leefsoq] in practical Jewish law [halakha] according to (any) one of them...""
Abraham ben ha-Rambam's 'INTRO. TO THE AGADA' as included in
""EN JACOB"" (Eheyn Ya'aqov) AGADA OF THE BABYLONIAN TALMUD, by Rabbi Jacob Ibn Chabib, revised and translated into English by R' S. H. Glick
""...And think not like those who do not grasp the real truth that every simple Derash or so-called allegorical explanation of the passage uttered by the sages, was handed over by tradition, like the principle parts of the Torah, because the fact is otherwise, that the explanation of such passages which do not involve either a dogma of a religious principle or any law of the Torah, has no traditional bearing, but was explained by the authors, merely according to their own (personal) knowledge and feeling,...
""...And many of them are used merely as figures of speech in a poetical style, or are explained in that poetical form. Thus I have no doubt that when R. Joshua said (Zebachim 116.) regarding the sentence (Ex. 18,1.) And Jethro heard. What did he hear? R. Joshua said, ""the war of Amalek."" 6) This is merely an opinion, not a tradition and is bringing of evidence to support his opinion proves that it is so, for in a tradition we need no evidence, furthermore, the fact that all other sages differ with him on this explanation proves this also,..."""