The Council of Nicaea
Forasmuch as there are certain persons who kneel on the Lord's Day and in the days of Pentecost, therefore, to the intent that all things may be uniformly observed everywhere (in every parish), it seems good to the holy Synod that prayer be made to God standing.
Source details
A.D. 325 · Canon 20 (325)
Checked word-for-word against Nicene and Post-Nicene Fathers, Series 2, Vol. 14 · 2026-07-26