Nor merely from anger, but altogether from all perturbation of mind, ought the exercise of prayer to be free, uttered from a spirit such as the Spirit unto whom it is sent. For a defiled spirit cannot be acknowledged by a holy Spirit, nor a sad by a joyful, nor a fettered by a free. No one grants reception to his adversary: no one grants admittance except to his compeer.
Reproduced in full. Translation: Ante-Nicene Fathers, vol. 3 (Roberts and Donaldson, 1885), public domain (Public domain).