When is a belief considered a law of the Torah and does it require a sabbath?

In the Gemara of Berakhot, regarding the obligation of benedictions, the Gemara said, “But it is not permissible for a person to enjoy it, etc.” The reader, Joshua, understands that this is from the Torah. In the sequence of reading the Gemara, it can be understood as follows: The Gemara simply states that the obligation is from the Torah, and we just need to find it. Didn’t we find it? Well, that’s good, because it is a simple explanation, and that’s what the Torah intended. He excuses the question of why one does not benediction in doubt by contradicting the law of “a blessing that is not necessary” (apparently, this in itself shows the weakness of the explanation in comparison to the law of the Torah).
According to him. Are there places where we see that a supposition (not absolute as in the blessings, for the apocrypha “let no sinner be rewarded”) has a law from the Torah?