I don't think it states that anywhere in scripture. I was just suggesting that Billy Graham and others have instituted that practice to avoid temptation and the appearance of temptation and improprieties. So, it's not scriptural exactly, but it is inferred from the meaning of scriptures such as 2 Timothy 2:22 (flee youthful lusts) and 1 Corinthians 6:18 (flee fornication).
Not every interaction with the opposite sex means we lust or fornicate.
Give me chastity and continence, but not yet --Saint Augustine.