Exodus 18:18

18:18 You will surely wear out, both you and these people who are with you, for this is too heavy a burden for you; you are not able to do it by yourself.

Exodus 19:23

19:23 Moses said to the Lord, “The people are not able to come up to Mount Sinai, because you solemnly warned us, ‘Set boundaries for the mountain and set it apart.’”