Hermas Shepherd of Hermas book 3 similitude 5.4 (60-120 ad)
[The Shepherd said:] “But those who are weak and slothful in prayer hesitate to ask anything from the Lord, but the Lord is full of compassion, and gives without fail to all who ask him. But you, [Hermas,] having been strengthened by the holy angel [you saw], and having obtained from him such intercession, and not being slothful, why do not you ask of the Lord understanding, and receive it from him?”
Hippolytus Against Plato, On the Cause of the Universe par 3 (170-236 ad)
No sleep will give them rest; no night will soothe them; no death will deliver them from punishment; no voice of interceding friends will profit them. For neither are the righteous seen by them any longer, nor are they worthy of remembrance.
Clement of Alexandria Stromata book 7 ch 12 (150-215 ad)
In this way is he [the true Christian] always pure for prayer. He also prays in the society of angels, as being already of angelic rank, and he is never out of their holy keeping, and though he pray alone, he has the choir of the saints standing with him [in prayer].
Origen on Prayer ch 20 (185-254 ad)
But not the high priest [Christ] alone prays for those who pray sincerely, but also the angels . . . as also the souls of the saints who have already fallen asleep.
Rylands Papyrus P470 Egypt (250 ad)
Under thy compassion we take refuge, O Mother of God (Theotokos). Do not despise our petitions in the time of trouble, but from dangers ransom us, singularly holy, singularly blessed.
Methodius of Olympus Oration on Simeon and Anna 14 (305 ad)         
Hail to you for ever, Virgin Mother of God, our unceasing joy, for to you do I turn again. You are the beginning of our feast; you are its middle and end; the pearl of great price that belongs to the kingdom; the fat of every victim, the living altar of the bread of life [Jesus]. Hail, you treasure of the love of God. Hail, you fount of the Son’s love for man. . . . You gleamed, sweet gift-bestowing Mother, with the light of the sun; you gleamed with the insupportable fires of a most fervent charity, bringing forth in the end that which was conceived of you . . . making manifest the mystery hidden and unspeakable, the invisible Son of the Father—the Prince of Peace, who in a marvelous manner showed himself as less than all littleness. Therefore, we pray [ask] you, the most excellent among women, who glories in the confidence of your maternal honors, that you would unceasingly keep us in remembrance. O holy Mother of God, remember us, I say, who make our boast in you, and who in august hymns celebrate the memory, which will ever live, and never fade away. And you also, O honored and venerable Simeon, you earliest host of our holy religion, and teacher of the resurrection of the faithful, do be our patron and advocate with that Savior God, whom you were deemed worthy to receive into your arms. We, together with you, sing our praises to Christ, who has the power of life and death, saying, “You are the true Light, proceeding from the true light; the true God, begotten of the true God” (ibid.).
Cyril of Jerusalem Catechetical Lecture 23 par 9 (315-386 ad)
Then we commemorate also those who have fallen asleep before us, first Patriarchs, Prophets, Apostles, Martyrs, that at their prayers and intercessions God would receive our petition. Then on behalf also of the Holy Fathers and Bishops who have fallen asleep before us, and in a word of all who in past years have fallen asleep among us, believing that it will be a very great benefit to the souls, for whom the supplication is put up, while that holy and most awful sacrifice is set forth.
Gregory Nazianzen Oration 18.4 (325- 389 ad)
Aye, I am well assured that his intercession is of more avail now than was his instruction in former days, since he is closer to God, now that he has shaken off his bodily fetters.
Basil Letter 360 (329-379 ad)
I acknowledge also the holy apostles, prophets, and martyrs; and I invoke them to supplication to God, that through them, that is, through their mediation, the merciful God may be propitious to me, and that a ransom may be made and given me for my sins. Wherefore also I honour and kiss the features of their images, inasmuch as they have been handed down from the holy apostles, and are not forbidden, but are in all our churches.
Ambrose of Milan Concerning Widows par 55 (340-397 ad)
So Peter and Andrew prayed for the widow. Would that there were some one who could so quickly pray for us, or better still, they who prayed for the mother-in-law, Peter and Andrew his brother. Then they could pray for one related to them, now they are able to pray for us and for all.
Ambrose of Milan Concerning Widows par 54 (340-397 ad)
“She was taken,” it is said, “with a great fever, and they besought him for her.” You too have those near you to entreat for you. You have the Apostles near, you have the Martyrs near; if associated with the Martyrs in devotion, you draw near them also by works of mercy. Do you show mercy and you will be close to Peter. It is not relationship by blood but affinity of virtue which makes near, for we walk not in the flesh but in the Spirit. Cherish, then, the nearness of Peter and the affinity of Andrew, that they may pray for you and your lusts give way.
John Chrysostom Homily 26 on Second Corinthians (347-407 ad)
He who wears the purple [i.e., a royal man] . . . stands begging of the saints to be his patrons with God, and he that wears a diadem begs the tentmaker [Paul] and the fisherman [Peter] as patrons, even though they be dead.
John Chrysostom Homily 3 on Second Timothy (347-407 ad)
And what wonder, if he who communicates to the living is thought worthy of the same rewards with those who contend, since it is possible to communicate after death even with the departed, with those who are asleep, who are already crowned, who want for nothing. For hear Paul saying, “Partaking in the memories of the Saints.” And how may this be done? When thou admirest a man, when thou doest any of those acts for which he was crowned, thou art evidently a sharer in his labors, and in his crowns.
Jerome against the Vigilantius par 6 (347-420 ad)
If Apostles and martyrs while still in the body can pray for others, when they ought still to be anxious for themselves, how much more must they do so when once they have won their crowns, overcome, and triumphed?
Augustine Reply to Faustus the Manichean Book 20 par 21 (354-430 ad)
It is true that Christians pay religious honor to the memory of the martyrs, both to excite us to imitate them and to obtain a share in their merits, and the assistance of their prayers.
Augustine Reply to Faustus the Manichean Book 20 par 21 (354-430 ad)
To sacrifice to the martyrs, even fasting, is worse than to go home intoxicated from their feast: to sacrifice to the martyrs, I say, which is a different thing from sacrificing to God in memory of the martyrs, as we do constantly, in the manner required since the revelation of the New Testament, for this belongs to the worship or latria which is due to God alone. But it is vain to try to make these heretics understand the full meaning of these words of the Psalmist: “He that offereth the sacrifice of praise glorifieth me, and in this way will I show him my salvation.” Before the coming of Christ, the flesh and blood of this sacrifice were foreshadowed in the animals slain; in the passion of Christ the types were fulfilled by the true sacrifice; after the ascension of Christ, this sacrifice is commemorated in the sacrament.
Augustine on the Holy Trinity Book 1 ch 6.13 (354-430 ad)
But that the Holy Spirit is not a creature is made quite plain by that passage above all others, where we are commanded not to serve the creature, but the Creator; not in the sense in which we are commanded to “serve” one another by love, which is in Greek douleuein, but in that in which God alone is served, which is in Greek latreuein. From whence they are called idolaters who tender that service to images which is due to God. For it is this service concerning which it is said, “Thou shalt worship the Lord thy God, and Him only shalt thou serve.” For this is found also more distinctly in the Greek Scriptures, which have latreuseis. Now if we are forbidden to serve the creature with such a service, seeing that it is written, the creature more than the Creator), then assuredly the Holy Spirit is not a creature, to whom such a service is paid by all the saints; as says the apostle, “For we are the circumcision, which serve the Spirit of God,” which is in the Greek latreuontes. For even most Latin copies also have it thus,
Augustine Exposition on Psalm 86 par 23 (354-430 ad)
For our Lord Jesus Christ still intercedeth for us: all the Martyrs who are with Him intercede for us.
Sozomen Ecclesial History Book 7 Ch 5 (375-477 ad)
For the power of God was there manifested, and was helpful both in waking visions and in dreams, often for the relief of many diseases and for those afflicted by some sudden transmutation in their affairs. The power was accredited to Mary, the Mother of God, the holy virgin, for she does manifest herself in this way.