Lay down the law

Six or eight thousand years ago / They laid down the law / In Mesopotamia

[I]n other words, some Jews thought of Moses as the one who laid down the Law, while others saw him more as a prophet.

He concluded this sentence with a self-important cough, as one who has laid down the law in an indisputable manner.

Montague could picture the grim, hawk-faced old man, sitting at the head of the council board, and laying down the law to the masters of the Metropolis.

Looks like the governor's laid down the law about the guards getting too lax, so we have to be damned careful.