Ezra 9:1-2 "After these things had been done, the leaders came to me and said, “The people of Israel, including the priests and the Levites, have not kept themselves separate from the neighboring peoples with their detestable practices, like those of the Canaanites, Hittites, Perizzites, Jebusites, Ammonites, Moabites, Egyptians and Amorites. 2 They have taken some of their daughters as wives for themselves and their sons, and have mingled the holy race with the peoples around them. And the leaders and officials have led the way in this unfaithfulness.”
"Now honor the Lord, the God of your ancestors, and do his will. Separate yourselves from the peoples around you and from your foreign wives.”
"Ezra-Nehemiah grapples with the marriage of Jews with unconverted people; conversion is not remotely hinted at," (pg. 84 of The Anchor Bible [Ezra]).
"It should be observed that the question of intermarriage does not exist in Ruth, because she had already become a convert, that is, first she turns to the faith of Naomi and becomes an Israelite, and then she marries," (ibid).