Pennington is currently in a Nashville hospital bed, undergoing treatment for a non-Hodgkin's double-hit lymphoma diagnosis, WZTV reported.
Collazo, 24, is a registered nurse at Tristar Centennial's Sarah Cannon Cancer Center in Nashville, according to The Tennessean. She started playing guitar in middle school but prefers to sing.
“I admitted (Pennington) to the hospital and we got to talking, so I asked him to tell me something fun about himself. I could tell he was kind of down,” Collazo told the newspaper. After they shared their musical experiences, Collazo brought in a guitar Sunday for Pennington to play.
"My dad's nurse, Alex, heard that he was a guitar player, so she brought her guitar for him to play during his chemotherapy treatments and sang 'O Holy Night' with him," Leath wrote in a Facebook post Sunday. "Who knew she could also sing."
Sunday night, the pair sang "Can't Help Falling in Love" first, before Pennington asked Collazo if she knew any Christmas songs, The Tennessean reported.
They decided on “O Holy Night,” and Leath recorded their slow, quiet rendition, the newspaper reported.
The video has been shared more than 4,000 times on Facebook.
"Any time you go in the hospital for cancer, it's automatically a downer. This was an escape, for a while. It was a good thing," Pennington told The Tennessean.
“Music is such a wonderful healer. I was completely, totally moved by this,” Leath told the newspaper.