Sotah 9b - Nachash Hakadmoni

The gemara says that the snake had a plan to kill Adam and marry Chava. Rashi in chumash comments that the snake tried to get adam to eat first, so that adam will die and chava will remain for the snake to marry. The maharsha has difficulty with this peshat because it seems pretty clear from the pesukim that the snake was trying to convince chava to actually eat from the tree in which case she would die first, so what was the snakes plan? Maharsha explains that Adam was told not to eat from the tree prior to chava being created. However, adam understood that chava was equally commanded in this mitzvah, and therefore passed on the message that Hashem said not to eat from the tree. Adam also added on his own that Hashem said not to even touch the tree. The snake believed that since chava was not around at the time of the command of Hashem, she would not be killed by eating from the tree, but knew that from the perspective of adam and chava they were equally obligated not to eat from the tree. His plan was to push chava into the tree, since in her mind she was not allowed to even touch the tree. When nothing happens by touching the tree he would convince her to eat from it, and then when adam sees that nothing happened when she ate from it, he would eat from it as well. Being that from the snakes perspective chava would not die from eating from it, adam would die and chava would remain for the snake to marry - pretty sly snake!

There is a machlokes Rambam and Ra'avad regarding the issur of Bal Tosif. The Ra'avad holds that it only applies to adding positive mitzvos, but the chachamim are allowed to add negative prohibitions (as we see they set up gezeiros). But the rambam says that the issur applies even to negative prohibitions, unless they specify that it is not d'oraysa. I quoted in Nasiach B'chukecha that the Minchas Chinuch (454) brings a support to the Rambam from the gemara in sanhedrin 29a that proves כל המוסיף גורע from the fact that adam adding on the prohibition to touch the tree caused the violation of eating from it. Clearly the gemara implies adam did something wrong. According to the Ra'avad it is difficult to see what he did wrong, since the Rabbonon have the jurisdiction to add prohibitions without specifying that they are Rabbinic in nature. But according to the Rambam that was precisely the mistake of Adam; his failure to specify the nature of the prohibition and that it is only Rabbinic led to all the problems.