Exodus 16:8

בשר לאכל FLESH TO EAT— but it does not add as it does in the next phrase לִשְׂבֹּעַ, “to satisfaction”; the Torah thus teaches us a rule of conduct — that one should not eat meat to satiety. And what did He see (what reason had He) that He made bread fall for them in the morning and flesh at evening? Because the bread they asked for was a proper thing to demand since it is impossible for a person to exist without bread; but meat they asked for improperly, for they had abundant cattle, and besides it was possible for them to exist without flesh. On this account He gave it to them at evening, at a time of (when it would cause them) trouble, a manner which was not favourable to them (Mekhilta; Yoma 75). אשר אתם מלינים עליו means [YOUR MURMURINGS] WHICH YOU MAKE others who hear you murmuring MURMUR AGAINST HIM.

וַיֹּ֣אמֶר מֹשֶׁ֗ה בְּתֵ֣ת יְהֹוָה֩ לָכֶ֨ם בָּעֶ֜רֶב בָּשָׂ֣ר לֶאֱכֹ֗ל וְלֶ֤חֶם בַּבֹּ֙קֶר֙ לִשְׂבֹּ֔עַ בִּשְׁמֹ֤עַ יְהֹוָה֙ אֶת־תְּלֻנֹּ֣תֵיכֶ֔ם אֲשֶׁר־אַתֶּ֥ם מַלִּינִ֖ם עָלָ֑יו וְנַ֣חְנוּ מָ֔ה לֹא־עָלֵ֥ינוּ תְלֻנֹּתֵיכֶ֖ם כִּ֥י עַל־יְהֹוָֽה׃

And Moshe said, This shall be, when the Lord shall give you in the evening meat to eat, and in the morning your fill of bread; when the Lord hears your murmurings which you murmur against him: and what are we? your murmurings are not against us, but against the Lord.