Canon LXXX
If any bishop, or presbyter, or deacon, or any of those who are enumerated in the list of the clergy, or a layman, has no very grave necessity nor difficult business so as to keep him from church for a very long time, but being in town does not go to church on three consecutive Sundays—three weeks—if he is a cleric let him be deposed, but if a layman let him be cut off.
Ancient Epitome of Canon LXXX.
If anyone without the constraint of necessity leaves his church for three Lord’s days, he shall be deprived of communion.
This is a renewal of canon xi. of Sardica (xiv. according to the numbering of Dionysius Exiguus.)