They devoted themselves to the teaching of the apostles and to the communal life, to the breaking of the bread and to the prayers. - Acts 2:42
Would the word “devoted” have been used to describe their gathering to the “breaking of the bread” (i.e. Eucharist) if they had only done so occasionally?
On the first day of the week when we gathered to break bread, Paul spoke to them because he was going to leave on the next day… - Acts 20:7
It does not say on the first Sunday of the month or a quarterly Sunday of the year, it says simply the first day of the week as if it happened every first day of the week.
In 1 Corinthians 11 there was a major problem with abuses at the Lord’s Supper. If this was only an occasional gathering then how could so many abuses have cropped up so quickly?
But every Lord’s day gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. - Didache ch. 14
One of the earliest non-Biblical Christian texts explicitly states that Christians should gather on Sunday to celebrate the Eucharist.
