Yevamot 6A

לאו דמחמר, ואפילו הכי לא דחי.

the reference is not to a situation where a father demanded that his child perform prohibited labor on Shabbat that entails karet. Rather, he instructed him to transgress the prohibition against driving a laden animal. Although it is prohibited to cause animals to work on Shabbat, this does not entail the penalty of karet, as it has the status of a regular prohibition. And this shows that if one’s father told him to desecrate Shabbat by driving a donkey, even so, the positive mitzva to honor one’s parents does not override the prohibition against driving a laden animal.

אלא דקיימא לן דאתי עשה ודחי לא תעשה, ליגמר מהכא דלא לידחי!

§ The Talmud asks: If so, rather than that principle in which we maintain that a positive mitzva comes and overrides a prohibition, let us derive from here that it does not override even a regular prohibition. Just as it was inferred above from the case of tzitzit, in which the positive mitzva overrides the prohibition against diverse kinds, that all other positive mitzvot similarly override any prohibition, perhaps one should infer from the case of honoring one’s parents that positive mitzvot do not override prohibitions at all.

וכי תימא, שאני לאוי דשבת דחמירי ⁠— והא תנא בעלמא קאי, ולא קפריך!

And if you say that one should not infer this from here, as the prohibitions of Shabbat are different in that they are more serious, and for this reason the mitzva to honor one’s parents does not override these prohibitions, this cannot be the case, as the tanna speaks generally of a father who instructs a son to perform a regular prohibition, not to desecrate Shabbat, and he does not raise any difficulty of this kind.