Every President of the United States has recited the oath of office as the official start of their presidency.
The oath is found in Article II of the Constitution. It contains 35 words and goes as follows:
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."
According to ABC News, George Washington reportedly added the words "so help me God" to the oath, and it has been said by every president except Theodore Roosevelt.
All but two presidents placed their hand on a Bible while saying the oath, according to the Joint Congressional Committee on Inaugural Ceremonies. John Quincy Adams took the oath upon a book of the law. Theodore Roosevelt did not use a Bible for his first inauguration.
In 2013, President Barack Obama took the oath using two Bibles, one owned by Abraham Lincoln and the other by Martin Luther King Jr.