21 Forasmuch then as the letter owed its origin to a false story, and contained no order that I should come to you, I concluded that it was not the wish of your Piety that I should come. For in that you gave me no absolute command, but merely wrote as in answer to a letter from me, requesting that I might be permitted to set in order the things which seemed to be wanting, it was manifest to me (although no one told me this) that the letter which I had received did not express the sentiments of your Clemency.
All knew, and I also stated in writing, as Montanus is aware, that I did not refuse to come, but only that I thought it unbecoming to take advantage of the supposition that I had written to you to request this favour, fearing also lest the false accusers should find in this a pretence for saying that I made myself troublesome to your Piety. Nevertheless, I made preparations, as Montanus also knows, in order that, should you condescend to write to me, I might immediately leave home, and readily answer your commands; for I was not so mad as to resist such an order from you.
When then in fact your Piety did not write to me, how could I resist a command which I never received? Or how can they say that I refused to obey, when no orders were given me? Is not this again the mere fabrication of enemies, pretending that which never took place? I fear that even now, while I am engaged in this defence of myself, they may allege against me that I am doing that which I have never obtained your permission to do. So easily is my conduct made matter of accusation by them, and so ready are they to vent their calumnies in despite of that Scripture, which says, 'Love not to slander another, lest you be cut off. '
Source: Apologia ad Constantium (New Advent)