Exodus 16:13

השליו THE QUAILS — a species of fowl which is very fatty (cf. Yoma 75b). היתה שכבת הטל THERE WAS A LAYER OF DEW — Consequently the dew was lying upon the Manna. In another passage, however, it says, (Numbers 11:9) “And when the dew came down [upon the camp at night, the manna fell upon it]” and so there was dew under the Manna! Thus we see that the dew fell upon the ground and the Manna fell upon it, and then dew fell again upon this, and so it was as though it were carefully packed in a chest (Yoma 75b).

וַיְהִ֣י בָעֶ֔רֶב וַתַּ֣עַל הַשְּׂלָ֔ו וַתְּכַ֖ס אֶת־הַֽמַּחֲנֶ֑ה וּבַבֹּ֗קֶר הָֽיְתָה֙ שִׁכְבַ֣ת הַטַּ֔ל סָבִ֖יב לַֽמַּחֲנֶֽה׃

And it came to pass, that at evening the quails came up, and covered the camp: and in the morning the dew lay round about the camp.