According to PRI:
Rashida Tlaib, an American-born Muslim of Palestinian descent, was sworn in with her left hand on her own copy of the Quran, though she considered using a 1734 English translation that belonged to Thomas Jefferson. And Ilhan Omar, who arrived in the US 23 years ago as a refugee fleeing Somalia’s war, used the Quran of her late grandfather, who helped raise her… For many Muslim Americans, the presence of a Quran is a symbolic moment.
It’s not the first time members of Congress have been sworn in using the Quran. In 2007, former Democratic Rep. Keith Ellison of Minnesota — who was the first Muslim elected to Congress — used Jefferson’s Quran for his ceremonial swearing-in. Omar was elected to Ellison’s old seat after he stepped down to run for state attorney general and won. And Omar used a Quran when she was sworn in to the Minnesota House two years ago.