Musar על שבת 296:7

And they said: Just as it is a commandment to say a thing that will be heard, so is it a commandment not to say a thing that will not be heard (Yebamoth 65b). And our Sages said, "Better that they (the sinners) should commit a wrong not knowing that it is a wrong, than that they should commit that wrong intentionally" (Shabbath 148b).