Biblical basis for claiming Eve was a virgin prior to the Fall In Against Heresies (book 3, chapter 22) Irenaeus attempts to draw a comparison between Eve and Mary similar to the comparison Paul draws between Adam and Christ.  He says that Mary obeyed in a state of virginity 


  But Eve was disobedient; for she did not obey when as yet she was a
  virgin.


And that Eve, having been disobedient, was made the cause of death to the entire human race and Mary, obeying in the same state of virginity, became the cause of salvation for the entire human race.

Hosts of questions come to mind but this specific question is:  Is there biblical ground to claim that Genesis 2:25 "And the man and his wife were both naked and were not ashamed." means that they had not yet had moral and lawful intercourse as man and wife (as Irenaeus asserts) even though the command to have intercourse came before the fall?
Adam and Eve did not have intercourse before the Fall (although they could have) because Genesis 4:1, which is after the Fall, is the first reported instance that "Adam knew Eve his wife: who conceived".

St. Thomas Aquinas, in Summa Theologica I q. 98 a. 2 ("Whether in the state of innocence there would have been generation by coition?") ad 2, summarizes St. Augustine's argument:


  As Augustine says (Gen. ad lit. ix, 4), our first parents did not come together in paradise, because on account of sin they were ejected from paradise shortly after the creation of the woman; or because, having received the general Divine command relative to generation, they awaited the special command relative to time.


Genesis 2:25 doesn't prove Eve was a virgin before the Fall. As St. Augustine writes in City of God bk. 14 ch. 17, Adam and Eve knew of their nakedness before the Fall, but it did not cause concupiscence and shame in them:


  "They were naked and were not ashamed," Genesis 2:25 — not that their nakedness was unknown to them, but because nakedness was not yet shameful, because not yet did lust move those members without the will's consent