Exodus 8:1

And the Lord spake unto Moses
Either whilst the plague upon the waters continued, or immediately upon the removal of it:

go unto Pharaoh, and say unto him, thus saith the Lord, let my
people go, that they may serve me;
mentioning neither time nor place, where, when, and how long they should serve him, for which their dismission was required, but insist on it in general.