But before the baptism let the baptizer fast, and the baptized, and whoever else can; but you shall order the baptized to fast one or two days before. But let not your fasts be with the hypocrites, for they fast on the second and fifth day of the week. Rather, fast on the fourth day and the Preparation (Friday).
Almsgiving therefore is a good thing, even as repentance from sin. Fasting is better than prayer, but almsgiving than both. And love covers a multitude of sins, but prayer out of a good conscience delivers from death. Blessed is every man that is found full of these. For almsgiving lifts off the burden of sin.
Wherefore let us forsake the vain doing of the many and their false teachings, and turn unto the word which was delivered unto us from the beginning, being sober unto prayer and constant in fastings, entreating the all-seeing God with supplications that He bring us not into temptation, according as the Lord said, The Spirit is indeed willing, but the flesh is weak.
Letter to Diognetus
The soul when poorly treated in the matter of food and drinks is improved; and so Christians when punished increase more and more daily.
Shepherd of Hermas
Every enquiry needs humility. Fast therefore, and you shall receive what you ask from the Lord.
“I tell you,” said he, “that this is not a fast, wherein you think to fast; but I will teach you what is a complete fast and acceptable to the Lord. Listen,” said he; “God desires not such a vain fast; for by so fasting unto God you shall do nothing for righteousness. But fast you [unto God] such a fast as this; do no wickedness in your life, and serve the Lord with a pure heart; observe His commandments and walk in His ordinances, and let no evil desire rise up in your heart; but believe God. Then, if you shall do these things, and fear Him, and control yourself from every evil deed, you shall live unto God; and if you do these things, you shall accomplish a great fast, and one acceptable to God. – ibid
This then is the way, that you shall keep this fast which you are about to observe. First of all, keep yourself from every evil word and every evil desire, and purify your heart from all the vanities of this world. If you keep these things, this fast shall be perfect for you. And thus shall you do. Having fulfilled what is written, on that day on which you fast you shall taste nothing but bread and water; and from your meats, which you would have eaten, you shall reckon up the amount of that day’s expenditure, which you would have incurred, and shall give it to a widow, or an orphan, or to one in want, and so shall you humble your soul, that he that has received from your humiliation may satisfy his own soul, and may pray for you to the Lord. If then you shall so accomplish this fast, as I have commanded you, your sacrifice shall be acceptable in the sight of God, and this fasting shall be recorded; and the service so performed is beautiful and joyous and acceptable to the Lord. – ibid
And if they hear that one of their number is imprisoned or afflicted on account of the name of their Messiah, all of them anxiously minister to his necessity, and if it is possible to redeem him they set him free. And if there is among them any that is poor and needy, and if they have no spare food, they fast two or three days in order to supply to the needy their lack of food. They observe the precepts of their Messiah with much care, living justly and soberly as the Lord their God commanded them.
Clement of Alexandria
“Fasting with prayer is a good thing.” Now fastings signify abstinence from all evils whatsoever, both in action and in word, and in thought itself.
We count fasting or kneeling in worship on the Lord’s day to be unlawful. We rejoice in the same privilege also from Easter to Whitsunday.
At fasts, moreover, and Stations, no prayer should be made without kneeling, and the remaining customary marks of humility; for (then) we are not only praying, but deprecating, and making satisfaction to God our Lord. Touching times of prayer nothing at all has been prescribed, except clearly “to pray at every time and every place.” – ibid
And thus Holy Scripture instructs us, saying, “Prayer is good with fasting and almsgiving.” For He who will give us in the day of judgment a reward for our labors and alms, is even in this life a merciful hearer of one who comes to Him in prayer associated with good works. Thus, for instance, Cornelius the centurion, when he prayed, had a claim to be heard. For he was in the habit of doing many alms-deeds towards the people, and of ever praying to God. To this man, when he prayed about the ninth hour, appeared an angel bearing testimony to his labors, and saying, “Cornelius, your prayers and your alms are gone up in remembrance before God.” Those prayers quickly ascend to God which the merits of our labors urge upon God. Thus also Raphael the angel was a witness to the constant prayer and the constant good works of Tobias, saying, “It is honorable to reveal and confess the works of God. For when you didst pray, and Sarah, I did bring the remembrance of your prayers before the holiness of God. And when you didst bury the dead in simplicity, and because you didst not delay to rise up and to leave your dinner, but didst go out and cover the dead, I was sent to prove you; and again God has sent me to heal you, and Sarah your daughter-in-law. For I am Raphael, one of the seven holy angels which stand and go in and out before the glory of God.”