Deuteronomy 17:16

Only let him not increase to him more than two horses, lest his princes ride upon them, and become proud, neglect the words of the law, and commit the sin of the captivity of Mizraim; for the Lord hath told you, By that way ye shall return no more.

you will not again This had been given as a commandment, even though it was not recorded. Some people explain this to refer to “you will never again…” [Exodus 14: 13], but the latter verse was not spoken in the sense of a commandment.

HE SHALL NOT MULTIPLY HORSES TO HIMSELF — “except what he needs for his carriage, in order that he cause not the people to return to Egypt, because horses were obtained from Egypt, as it is said, And a chariot came up and went out of Egypt for six hundred shekels of silver, and a horse for a hundred and fifty.” This is Rashi’s language. But I have this difficulty regarding it, for the Rabbis have said in Yerushalmi at the end of Tractate Sanhedrin: “You may not return there for settlement, but you may return for business, for goods, and for conquest of the land.” And so, if the king should send men and buy horses and chariots there, it would be considered “trading” and would be permissible! It is then possible that Scripture admonishes [the king] not to increase his numbers of horses even from his own Land, or from the land of Shinar, or by way of permissible trading, in order that he should not put his trust in his chariots, because they are many, and in his horsemen, because they are exceedingly mighty, but his trust shall be in the Name of the Eternal. Then he admonishes the king not to cause the people to return to Egypt, to have his servants and people there as overseers of cattle dwelling in the cities for the chariots to the end that he should multiply horses, similar to what is said of Solomon, and all the store-cities that Solomon had, and the cities for his chariots etc. And thus he had in Egypt, as it is said, And the horses which Solomon had, were brought out of Egypt; also out of Keveh, the king’s merchants buying them etc. for no one was allowed to export horses from Egypt without permission from the Egyptian king and they paid him a tax for them. To Solomon, however, Pharaoh gave the right to export horses, meaning that he could take them out at will, and he could transfer that right to whomever he wished and keep the tax. He also had merchants stationed in Egypt buying all horses and sending to their lord [Solomon] those that he wanted and selling the others to kings of other countries. Thus it is said and so for all the kings of the Hittites, and for the kings of Aram, did they bring them out by their means, that is to say, they took them out through Solomon’s merchants, and it was to him that they gave the tax.