Origen quotes the Deuterocanon in support of the Intercession of Saints

But these pray along with those who genuinely pray—not only the high priest but also the angels who “rejoice in heaven over one repenting sinner more than over ninety-nine righteous that need not repentance,” and also the souls of the saints already at rest. Two instances make this plain. The first is where Raphael offers their service to God for Tobit and Sarah. After both had prayed, the scripture says, “The prayer of both was heard before the presence of the great Raphael and he was sent to heal them both,” and Raphael himself, when explaining his angelic commission at God’s command to help them, says:

“Even now when you prayed, and Sarah your daughter-in-law, I brought the memorial of your prayer before the Holy One,” and shortly after, “I am Raphael, one of the Seven angels who present the prayers of saints and enter in before the glory of the Holy One. Thus, according to Raphael’s account at least, prayer with fasting and almsgiving and righteousness is a good thing.

The second instance is in the Books of the Maccabees where Jeremiah appears in exceeding “white haired glory” so that a wondrous and most majestic authority was about him, and stretches forth his right hand and delivers to Judas a golden sword, and there witnesses to him another saint already at rest saying, “This is he who prays much for the people and the sacred city, God’s prophet Jeremiah.” For it is absurd when knowledge, though manifested to the worthy through a mirror and in a riddle for the present, is then revealed face to face not to think that the like is true of all other excellences as well, that they who prepare in this life beforehand are made strictly perfect then.

Origen
On Prayer
Chapter VI

The departed saints join in our prayers

Yet there is a certain helpful charm in a place of prayer being the spot in which believers meet together. Also it may well be that the assemblies of believers also are attended by angelic powers, by the powers of our Lord and Savior himself, and indeed by the spirits of saints, including those already fallen asleep, certainly of those still in life, though just how is not easy to say.

And if Paul, while still wearing the body, believed that he assisted in Corinth with his spirit, we need not abandon the belief that the blessed departed in spirit also, perhaps more than one who is in the body, make their way likewise into the churches. For that reason we ought not to despise prayer in churches, recognizing that it possesses a special virtue for him who genuinely joins in.

Origen
On Prayer
Chapter XX

The order of private prayer

In the beginning and opening of prayer, glory is to be ascribed according to one’s ability to God, through Christ who is to be glorified with Him, and in the Holy Spirit who is to be proclaimed with Him.

Thereafter, one should put thanksgivings: common thanksgivings—into which he introduces benefits conferred upon men in general—and thanksgivings for things which he has personally received from God. After thanksgiving it appears to me that one ought to become a powerful accuser of one’s own sins before God and ask first for healing with a view to being released from the habit which brings on sin, and secondly for forgiveness for past actions. After confession it appears to me that one ought to append as a fourth element the asking for the great and heavenly things, both personal and general, on behalf of one’s nearest and dearest. And last of all, one should bring prayer to an end ascribing glory to God through Jesus Christ in the Holy Spirit. As I already said, I have found these points scattered throughout the scriptures.

Origen
On Prayer
Chapter XX

Praying facing East is the ancient Christian tradition

Of the four directions, the North, South, East, and West, who would not at once admit that the East clearly indicates the duty of praying with the face turned towards it with the symbolic suggestion that the soul is looking upon the dawn of the true light?

Should anyone, however, prefer to direct his intercessions according to the aperture of the house, whichever way the doors of the house may face, saying that the sight of heaven appeals to one with a certain attraction greater than the view of the wall, and the eastward part of the house having no opening, we may say to him that since it is by human arrangement that houses are open in this or that direction but by nature that the East is preferred to all the other directions, the natural is to be set before the artificial. Besides, on that view why should one who wished to pray when in the open country pray to the East in preference to the West? If, in the one case it is reasonable to prefer the East, why should the same not be done in every case? Enough on that subject.

Origen
On Prayer
Chapter XX

Christ receives the prayers of the saints

For as much, then, as there is but one Son of man whose advent is placed between the two issues of catastrophe and promise, it must needs follow that to that one Son of man belong both the judgments upon the nations, and the prayers of the saints.

Tertullian
The Five Books Against Marcion, Book IV
Chapter XXXIX

Christ is the only God

For the prayer which He has taught us suits, as we have proved, none but the Creator. It is, of course, another matter if He does not wish to be prayed to, because He is the supremely and spontaneously good God! But who is this good God? There is, He says, “none but one.” It is not as if He had shown us that one of two gods was the supremely good; but He expressly asserts that there is one only good God, who is the only good, because He is the only God.

Tertullian
The Five Books Against Marcion, Book IV
Chapter XXXVI

The hours of prayer

Now, if some assign definite hours for prayer— as, for example, the third, and sixth, and ninth— yet the Gnostic prays throughout his whole life, endeavoring by prayer to have fellowship with God. And, briefly, having reached to this, he leaves behind him all that is of no service, as having now received the perfection of the man that acts by love. But the distribution of the hours into a threefold division, honored with as many prayers, those are acquainted with, who know the blessed triad of the holy abodes.

Clement of Alexandria
The Stromata, Book VII
Chapter VII