John Gill Commentary Ezra 9:11

"which thou hast commanded by thy servants the prophets, saying, The land, unto which ye go to possess it, is an unclean land through the uncleanness of the peoples of the lands, through their abominations, which have filled it from one end to another with their filthiness:" — Ezra 9:11 (ASV)

Which you have commanded by your servants the prophets
Moses, and Joshua, and others, see (Deuteronomy 7:3) (Joshua 23:12) (Judges 2:2)

saying, the land, to which you go to possess it ;
meaning the land of Canaan:

is an unclean land with the filthiness of the people of the lands,
with their abominations, which have filled it from one end to another
with their uncleanness ;
which is to be understood not of their idolatries only, but of their incestuous marriages, and impure copulations, on which account the Lord spewed out the old inhabitants of it; for which reason the Jews ought to have been careful not to have defiled it again by similar practices; see (Leviticus 18:1–30) .