Luke 2:3

And it came to pass in those days, that there went out a decree from Caesar Augustus, that all the world should be taxed.

(And this taxing was first made when Cyrenius was governor of Syria.)

And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, unto the city of David, which is called Bethlehem; (because he was of the house and lineage of David:)

To be taxed with Mary his espoused wife, being great with child.