"But offer to God a fasting of the following kind: Do no evil in your life, and serve the Lord with a pure heart: keep His commandments, walking in His precepts, and let no evil desire arise in your heart; and believe in God. If you do these things, and fear Him, and abstain from every evil thing, you will live unto God; and if you do these things, you will keep a great fast, and one acceptable before God."Hermas
The Shepherd Bk. 3 Pt. 1 Ch. I, Vol. 2

"Subsequently, fleeing from threatening Jezebel, after one single (meal of) food and drink, which he had found on being awakened by an angel, he too himself, in a space of forty days and nights, his belly empty, his mouth dry, arrived at Mount Horeb; where, when he had made a cave his inn, with how familiar a meeting with God was he received! “What (doest) thou, Elijah, here?” (1Ki_19:9, 1Ki_19:13.) Much more friendly was this voice than, “Adam, where art thou?” (Genesis 3:9, LXX) For the latter voice was uttering a threat to a fed man, the former soothing a fasting one. Such is the prerogative of circumscribed food, that it makes God tent-fellow (Cf. Mat_17:4; Mar_9:5; Luk_9:33) with man - peer, in truth, with peer! For if the eternal God will not hunger, as He testifies through Isaiah, this will be the time for man to be made equal with God, when he lives without food."Tertullian
Fasting Ch. VI, Vol. 4

"If any bishop, or presbyter, or deacon, or reader, or singer, does not fast the fast of forty days, or the fourth day of the week, and the day of the Preparation, let him be deprived, except he be hindered by weakness of body. But if he be one of the laity, let him be suspended."Constitution of the Apostles
Bk. 8 Pt. 2 Ch. XLVII, Vol. 7

"Now fasting’s signify abstinence from all evils whatsoever, both in action and in word, and in thought itself. As appears, then, righteousness is quadrangular; on all sides equal and like in word, in deed, in abstinence from evils, in beneficence, in gnostic perfection; nowhere, and in no respect halting, so that he does not appear unjust and unequal. As one, then, is righteous, so certainly is he a believer. But as he is a believer, he is not yet also righteous - I mean according to the righteousness of progress and perfection, according to which the Gnostic is called righteous."Clement
Stromata Bk 6 Chap. XII; Vol 2

"This fasting,” he continued, “is very good, provided the commandments of the Lord be observed. Thus, then, shall you observe the fasting which you intend to keep. First of all, be on your guard against every evil word, and every evil desire, and purify your heart from all the vanities of this world. If you guard against these things, your fasting will be perfect."Hermas
The Shepherd Bk. 3 Pt. 1 Ch. III, Vol. 2

"Therefore, after you have kept the festival of Pentecost, keep one week more festival, and after that fast; for it is reasonable to rejoice for the gift of God, and to fast after that relaxation: for both Moses and Elijah fasted forty days, and Daniel for “three weeks of days did not eat desirable bread, and flesh and wine did not enter into his mouth.” (Exo_34:28; 1Ki_19:8; Dan_10:2, Dan_10:3) And blessed Hannah, when she asked for Samuel, said: “I have not drunk wine nor strong drink, and I pour out my soul before the Lord.” (1Sa_1:15) And the Ninevites, when they fasted three days and three nights, (Jon_3:5) escaped the execution of wrath. And Esther, and Mordecai, and Judith, (Est_4:16; Judith 8:6) by fasting, escaped the insurrection of the ungodly Holofernes and Haman. And David says: “My knees are weak through fasting, and my flesh faileth for want of oil.” (Psa_109:24) Do you therefore fast, and ask your petitions of God. We enjoin you to fast every fourth day of the week, and every day of the preparation, and the surplusage of your fast bestow upon the needy; every Sabbath-day excepting one, and every Lord’s day, hold your solemn assemblies, and rejoice: for he will be guilty of sin who fasts on the Lord’s day, being the day of the resurrection, or during the time of Pentecost, or, in general, who is sad on a festival day to the Lord. For on them we ought to rejoice, and not to mourn."Constitution of the Apostles
Bk. 5 Pt. 2 Ch. XX, Vol. 7