Letter 550: Theodore Studite, Letter 550; Greek heading: Ἰωάννῃ κληρικῷ.

We have received the gift of your love, most genuine friend. But as for the request which you made, namely, in case you should happen to dine together with heretics, to know the penance [epitimion, the prescribed ecclesiastical penalty] for it, this we say: that for every sin worthy repentance obtains forgiveness; yet it is not permissible to lay down penances before the sin and thereby to open the door of sin. For if you should even ask, "Should I happen to commit fornication, against my will, what is the penance?", it is not right for me to answer you that (for it becomes an incitement to sin); rather this is what must be answered: do not commit the sin, nor dash your foot against a stone [cf. Psalm 91:12], either in the intellectual or in the perceptible sense. But when you have stumbled, then the physician gives the healing remedy to the one who entreats and repents. These things I have written to you with much attentiveness, praying that you may be delivered, beloved, from every evil.