Question

In the Talmud in Berakhot, regarding the obligation to recite blessings, the Talmud says: “Rather, it is reasoning: it is forbidden for a person to derive benefit…” The Pnei Yehoshua understands that this reasoning is of Torah-level status. From the flow of the Talmudic discussion, that does seem plausible: it is obvious to the Talmud that the obligation is from the Torah, and it only needs to locate the source. Couldn’t find one? Fine — because this is simple reasoning, and that is what the Torah intended. The difficulty of why, in a case of doubt, one does not recite the blessing, he answers by saying that it conflicts with the rule of “an unnecessary blessing” — which seemingly itself shows the weakness of this reasoning compared to an actual Torah-level law.
According to his view: are there places where we see that reasoning (not something absolute as in blessings, unlike “so that a sinner should not profit”) has the status of Torah law?