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