תּלמוד אויף אסתר 1:3

In those days, when the king sat [on his throne] (Esther 1:2). But it says just afterwards, “In the third year of his reign? Rav said: What is meant by “when he sat”? After he began to feel secure. He reasoned thus: Belshazar calculated and made a mistake; I have calculated and made no mistake.

“The army of Persia and Media, the governors” (Esther 1:3). But elsewhere it is written, [The chronicles] of the kings of Media and Persia” (Esther 10:2). Rava said: They [the Medes and Persians] made a stipulation with one another, saying, if we supply the kings, you will supply the Governors, and if you supply the kings we will supply the Governors.