First Council of Nicaea, Canon XII

As many as were called by grace, and displayed the first zeal, having cast aside their military girdles, but afterwards returned, like dogs, to their own vomit, (so that some spent money and by means of gifts regained their military stations); let these, after they have passed the space of three years as hearers, be for ten years prostrators.  But in all these cases it is necessary to examine well into their purpose and what their repentance appears to be like.  For as many as give evidence of their conversions by deeds, and not pretence, with fear, and tears, and perseverance, and good works, when they have fulfilled their appointed time as hearers, may properly communicate in prayers; and after that the bishop may determine yet more favourably concerning them.  But those who take [the matter] with indifference, and who think the form of [not] entering the Church is sufficient for their conversion, must fulfil the whole time.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.