Kyrsten Sinema chose not to hold the traditional Bible when she was sworn in Thursday as a U.S. senator from Arizona. Instead, she held a copy of the Constitution.

A spokesperson for the first-term Democrat said she chose to use a book from the Library of Congress that contains the texts of the Arizona and U.S. Constitutions, reports azcentral.com.

"Kyrsten always gets sworn in on a Constitution simply because of her love for the Constitution," Sinema spokesman John LaBombard told the local news outlet.

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He didn't comment on the senator's religious beliefs. Sinema is the only person in Congress to state that she is "religiously unaffiliated," according to the Pew Research Center for Religion & Public life.

Sen. Sinema holds a copy of the constitution as she is sworn in by Vice President Mike Pence during the swearing-in re-enactments Thursday. Alex Edelman / AFP/Getty Images

Sinema, the first female U.S. senator from Arizona, is seen holding the book in a video of the swearing-in re-enactment with Vice President Mike Pence.

In the video, Mr. Pence finishes saying the senator's oath with the customary words "so help you God?" Sinema responds, "I do."

She isn't the only person who opted for a different book for the event. Over a dozen books and documents were chosen for the ceremony, according to CNN.