Babylonian Talmud, Megillah 13a

So Esther was taken unto king Ahasuerus into his house royal in the tenth month, which is the (cold winter) month of Tebeth, the month when body takes pleasure in (the warmth of) another body. And the king loved Esther above all the women, and she obtained grace and favour in his sight more than all the virgins. [Translation by Rabbi Steve Greenberg]