THE SABBATH PUZZLE

I have come across the following little poser in an old book. I wonder how many readers will see the author's intended solution to the riddle. 

Christians the week's first day for Sabbath hold;
The Jews the seventh, as they did of old;
The Turks the sixth, as we have oft been told.
How can these three, in the same place and day,
Have each his own true Sabbath? tell, I pray.