Ok, I found it. It is a quote from the ???? ?????. This midrash was compiled in the 14th century, but was only brought to general attention in the 1800’s. They have it on otsar hachochma, but not on bar ilan. It is in ???? ????, on page 60 of the edition published by Dovid Tzvi Hoffman.
Here is what it says: It is on the passuk of ?? ???? ????? ????, and the obvious question is how does Hashem know what Pharoh will say?
The Midrash says: this is what the navi means when he says Hashem is ???? ???? ?? ????. This passuk is a praise of the awesomeness of Hashem, that when He creates a child, he knows how many words the person will say in their lifetime, and what those words will be.
The midrash continues: And not only that, but Hashem also knows how many times you will stand up and sit down, and how many steps you will take. As the passuk says ??? ???? ???? ?????, and ?? ??? ???? ?????. And not only those obvious things, but even what is hidden Hashem knows, that is: your thoughts, as it says ??? ? ???? ??.
So, so sum up: This midrash is just saying that Hashem knows how many words you will speak in your life; not that your life is shorter if say words. If you really think so, then you should follow the entire thing, and say that since Hashem also knows how many thoughts, steps, sitting downs, and getting ups you will do, each of those also shorten your life. Good luck not thinking anymore; maybe sleep all day.
Please everyone: stop teaching your kids narishkeit. I don’t think narishkeit shortens your life, but it sure makes it less fulfilling. (Also, did you all notice how I said as a joke last night that it should apply to steps you take, and that is exactly what the midrash does say–that it is the same.)