On Prayer by Tertullian
Chapter XVIII.--Of the Kiss of Peace.
Another custom has now become prevalent. Such as are fasting withhold the kiss of peace, which is the seal of prayer, after prayer made with brethren. But when is peace more to be concluded with brethren than when, at the time of some religious observance, our prayer ascends with more acceptability; that they may themselves participate in our observance, and thereby be mollified for transacting with their brother touching their own peace? What prayer is complete if divorced from the |holy kiss?| Whom does peace impede when rendering service to his Lord? What kind of sacrifice is that from which men depart without peace? Whatever our prayer be, it will not be better than the observance of the precept by which we are bidden to conceal our fasts; for now, by abstinence from the kiss, we are known to be fasting. But even if there be some reason for this practice, still, lest you offend against this precept, you may perhaps defer your |peace| at home, where it is not possible for your fast to be entirely kept secret. But wherever else you can conceal your observance, you ought to remember the precept: thus you may satisfy the requirements of Discipline abroad and of custom at home. So, too, on the day of the passover, when the religious observance of a fast is general, and as it were public, we justly forego the kiss, caring nothing to conceal anything which we do in common with all.