Exodus 18:14

And when Moses’ father in law saw all that he did to the people, he said, What is this thing that thou doest to the people? why sittest thou thyself alone, and all the people stand by thee from morning unto even?

Cross-reference

Exodus 18:17 gives Jethro's direct response: what Moses is doing is not good—setting up the delegation plan.

Exodus 18:26 shows the fulfillment of Jethro's advice—now judges handle small cases, Moses only hard cases.