Deuteronomy 1:9

And I spake unto you at that time,.... About that time; for it was after the rock in Horeb was smitten, and before they encamped at Mount Sinai, that Jethro gave the advice which Moses took, and proceeded on it, as here related; see Exodus 18:1

saying, I am not able to bear you myself alone; to rule and govern them, judge and determine matters between them. Jethro suggested this to Moses, and he took the hint, and was conscious to himself that it was too much for him, and so declared it to the people, though it is not before recorded; see Exodus 18:18.