On Prayer by Tertullian
Chapter XXIII.--Of 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 offence 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. Similarly, too, in the period of Pentecost; which period we distinguish by the same solemnity of exultation. But who would hesitate every day to prostrate himself before God, at least in the first prayer with which we enter on the daylight? 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.|