Plutarch, Life of Lycurgus of Sparta 6:

So eager was Lycurgus for the establishment of this form of government, that he obtained an oracle from Delphi about it, which they call a 'rhetra'. And this is the way it runs:

When thou has built a temple to Zeus Syllanius and Athena Syllania, divided the people into phylai, and divided them into 'obai', and established a Gerousia of thirty including the Archagetai, then from time to time 'appellazein' between Babyka and Knakion, and there introduce and repeal measures; but the Demos must have the decision and the power.

In these clauses, the phylai and obai refer to divisions and distributions of the people into parts, some of which are named clans and others obes. By Archagetai the Kings are meant, and 'appellazein' means 'to assemble' the people, and that the beginning and cause of the constitution was the Pythian. The Babyka is now called Cheimarros, and the Knakion the Oineus; but Aristotle says that the Knakion is a river and Babyka is a bridge. Between these they held their assemblies, having neither halls nor any other kind of building for the purpose. For thus Lycurgus thought that good counsel (eubouleia) was not promoted, but rather discouraged, since the serious purposes of an assembly were rendered foolish and futile by vain thoughts, as they gazed upon statues, and paintings, or scenic embellishments ('proscenia of theaters'), or extravagantly decorated roofs of Bouleuteria. When the multitude was assembled thus, no one of them was permitted to make a motion, but the motion laid before them by the Gerontes and Kings could be accepted or rejected by the Demos.

Later, however, when the Demos, by additions and subtractions perverted and distorted the sense of motions laid before them, the Kings Polydoros and Theopompos inserted the following clause in the Rhetra:

But if the Demos should choose badly, the Gerontes and Kings shall be 'apostateres'

That is, the should not ratify the vote, but dismiss and dissolve the Assembly outright, on the ground that it was perverting and changing the motion contrary to the best interests of the state. And they were actually able to persuade the city that the God authorized this addition to the Rhetra, as Tyrtaeus recalls in these verses:

Phoebus Apollo's the mandate was which they brought from Pytho
Voicing the will of the God, nor were his words unfulfilled:
Sway in the Boule and divine honors belong to the Kings
Under whose care has been set Sparta's city of charm;
Second to them are the Gerontes, and then come the men of the people
duly confirming the straight rhetrai.