Constantine's Letter to Eusebius concerning Mambre
Victor Constantinus, Maximus Augustus, to Macarius, and the rest of the bishops in Palestine.
One benefit, and that of no ordinary importance, has been conferred on us by my truly pious mother-in-law, in that she has made known to us by letter that abandoned folly of impious men which has hitherto escaped detection by you: so that the criminal conduct thus overlooked may now through our means obtain fitting correction and remedy, necessary though tardy. For surely it is a grave impiety indeed, that holy places should be defiled by the stain of unhallowed impurities. What then is this, dearest brethren, which, though it has eluded your sagacity, she of whom I speak was impelled by a pious sense of duty to disclose?
Source: Life of Constantine (New Advent)