Ascetic struggle aids in prayer

In the first place, it is the affliction of the flesh—a victim able to appease the Lord by means of the sacrifice of humiliation—in making a libation to the Lord of sordid raiment, together with scantiness of food, content with simple diet and the pure drink of water in conjoining fasts to all this; in inuring herself to sackcloth and ashes.  This bodily patience adds a grace to our prayers for good, a strength to our prayers against evil; this opens the ears of Christ our God, dissipates severity, elicits clemency.

…That which springs from a virtue of the mind is perfected in the flesh; and, finally, by the patience of the flesh, does battle under persecution.

Tertullian 
On Patience
Chapter XIII

Traditions regarding kneeling

In the matter of kneeling also prayer is subject to diversity of observance, through the act of some few who abstain from kneeling on the Sabbath; and since this dissension is particularly on its trial before the churches, the Lord will give His grace that the dissentients may either yield, or else indulge their opinion without offense to others. We, however (just as we have received), only on the day of the Lord’s Resurrection ought to guard not only against kneeling, but every posture and office of solicitude; deferring even our businesses lest we give any place to the devil.

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.”

Tertullian
On Prayer
Chapter XXII

On fasting and the Eucharist

Similarly, too, touching the days of Stations, most think that they must not be present at the sacrificial prayers, on the ground that the Station must be dissolved by reception of the Lord’s Body. Does, then, the Eucharist cancel a service devoted to God, or bind it more to God?  Will not your Station be more solemn if you have withal stood at God’s altar? When the Lord’s Body has been received and reserved each point is secured, both the participation of the sacrifice and the discharge of duty.

Tertullian
On Prayer
Chapter XIX

Masses for the dead, fasting, kneeling and the sign of the cross during worship

As often as the anniversary comes round, we make offerings for the dead as birthday honors. 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. We feel pained should any wine or bread, even though our own, be cast upon the ground.  At every forward step and movement, at every going in and out, when we put on our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign.

If, for these and other such rules, you insist upon having positive Scripture injunction, you will find none. Tradition will be held forth to you as the originator of them, custom as their strengthener, and faith as their observer. That reason will support tradition, and custom, and faith, you will either yourself perceive, or learn from some one who has.

…This instances, therefore, will make it sufficiently plain that you can vindicate the keeping of even unwritten tradition established by custom; the proper witness for tradition when demonstrated by long-continued observance.

Tertullian
The Chaplet
Chapter III and IV