Sabbath vs. Sunday Debate: Ultimate Question

And the next sabbath day came almost the whole city together to
hear the word of God. Acts 13:44

Q: "So if Sunday were the day to keep holy, where is the record of apostolic instruction saying that?
---This is strange indeed. 

One searches the New Testament in vain, not simply for a Sunday command, but for any formula of service, any suggestion of holiness to the day, any counsel on the proper way of living for that day. 

The point bears repeating: 

The churches raised up among the gentiles would never have stumbled onto the idea of Sunday sacredness from reading what the apostles wrote." 

F.D. Nichols