Greenville, South Carolina CNN  — 

Republican presidential candidate Ben Carson celebrated his birthday Friday by poking fun at front-runner Donald Trump.

“I guess the best birthday present is I heard Donald Trump had dropped out,” he joked Friday at Heritage Action for America’s presidential forum in Greenville, South Carolina.

“Oh, wait a minute. That was just for today,” Carson said.

Trump at the last minute canceled his appearance at the conservative forum, citing the need to close “a significant business transaction” that was delayed.

Trump’s cancellation came after he took fire for refusing Thursday to address an attendee’s assertion that Muslims are a “problem” in America and that President Barack Obama is a Muslim during a campaign event in New Hampshire.

Trump’s campaign manager told CNN that Trump did not hear the questioner make those statements and only heard the questioner ask about Muslim terrorist training camps in the U.S.

“All he heard was a question about training camps, which he said we have to look into,” campaign manager Corey Lewandowski said. “The media want to make this an issue about Obama, but it’s about him waging a war on Christianity.”