In the korbanos reading of the morning service, they all begin with vayomer h' el moshe l'emor... except the ketores which skips l'emor, saying only vayomer h' el moshe kach lcha...
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The expression לאמר is normally understood to imply that the statement following has to be said over to others. See for example Ramban on Shemos 6 (10):
אמרו המפרשים כי מלת לאמר בכל התורה לאמר לישראל
The commentators say that the word לאמר generally in the Torah means that the the statement following has to be said over to the Jewish people.
Now the verse for the ketores says
וַיֹּאמֶר ה' אֶל משֶׁה קַח לְךָ סַמִּים
And the L-rd said to Moses: "Take for yourself aromatics, ...”
Take for yourself so Moshe did not have to tell this instruction (take aromatics) to anyone else. So therefore the verse does not contain the word לאמר .
Hat-tip to @kouty.