St Ignatius (Brianchaninov). "Paterikon".
A presbyter (hieromonk) Abba Eulogios, while celebrating the Holy Liturgy, was overwhelmed by the Divine Grace so much, that he could see the spiritual condition of anyone who came to him. Often he forbade to some monks who drew near to take the Holy Communion, saying, ‘How dare you draw near the Holy Communion, having unclean thoughts? This night you enjoyed unclean lustful thoughts, thinking, that both an unclean sinner and a pure man can draw near the Grace of Christ’. He also rebuked other people of different sins. ‘Do not take the Holy Communion for a short time,’ he used to say to them, ‘and repent sincerely to have your sins be pardoned and you became worthy of the Communion with God. The man who does not repudiate any communion with sinful thoughts cannot draw near to the Holy Mysteries of God.’
The communion with sinful thoughts means agreeing and enjoying them by one’s own will, but not the involuntary submission to their flood: the second cannot be avoided, but anyone can withstand them.