Правило 67 Василия Великого
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Incest between brother and sister requires the time of repentance reserved for a murderer.
This rule speaks of fornication between brother and sister, descended from the same father and mother, which is in the strict sense of the word άδελφομιξία, and determines the same punishment for the perpetrators as for free murderers, i.e. twenty years' excommunication from Holy Communion, of course, only if they renounced their wicked deed. We mention this because the same St. the father determines, by his 76 rule, a different punishment for brother and sister who do not come from the same father and mother.
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