Michael Phelps posted a photo of a Vegas concert on Instagram Monday, the day after a gunman opened fire on some 22,000 people at an outdoor concert Sunday night in the deadliest mass shooting in modern U.S. history.

According to the photo, Phelps attended the three-day country music festival Friday with his wife Nicole.

The Olympic swimmer said he woke up Monday morning to messages from friends and family asking if he and his wife were safe and at home.

(This is a photo taken from Friday night) Nicole and I were there with friends on Friday... I woke up this am with texts from a friends and family members making sure we were home and safe... My thoughts and prayers out to the affected family members and friends. #prayforlasvegas

A post shared by Michael Phelps (@m_phelps00) on

On Sunday night, 64-year-old Stephen Paddock opened fire from a hotel room above a packed, outdoor concert in Las Vegas, killing at least 59, wounding 527 more.

Phelps, his wife and their son live here in the Valley. The winner of 23 Olympic gold medals moved to Arizona in 2015 when his coach Bob Bowman was hired as head coach for Arizona State University swim team.

"My thoughts and prayers out to the affected family members and friends. #prayforlasvegas," Phelps said in the Instagram caption.