Rashi on Deuteronomy 17:16/רש"י על דברים י״ז:ט״ז

1לא ירבה לו סוסים HE SHALL NOT MULTIPLY HORSES TO HIMSELF — but he shall have only what is sufficient for his carriages, in order that he shall not cause the people to return to Egypt, because horses come from there, as it is said in the history of Solomon (1 Kings 10:29) “And a chariot came up and went out of Egypt for six hundred shekels of silver and a horse for a hundred and fifty” (Sanhedrin 21b).