Republican presidential candidate Ben Carson on Friday apologized for questioning fellow primary challenger Donald Trump’s spiritual faith, drawing further contrast on how top GOP candidates handle the front-running Trump's calculated and often withering attacks. 

“I think I did slip, and that’s why I apologized,” Carson said on Fox News’ “On the Record with Greta Van Susteren.” “There is no reason ever to question anybody’s faith. That’s something between them and God.”

A few days earlier, Carson said he didn’t get the impression that humility and “fear of the Lord” were important to Trump.

“Maybe I'm wrong, but I don't get that," said Carson, a retired neurosurgeon whose soft-spoken style has made him a top 2016 GOP presidential candidate.

Carson made the apology just hours before Trump -- whose has declined to apologize numerous times during his campaign for questionable remarks about fellow candidates, Mexicans and others -- suggested he has no immediate plans to ever apologize.

“I fully think apologizing is a great thing," the front-running GOP candidate and billionaire businessman said on NBC’s “Tonight Show. “But you have to be wrong. ... I will absolutely apologize sometime in the hopefully distant future if I'm ever wrong."

Most recently, Trump seemed to criticize the physical appearance of surging GOP contender Carly Fiorina in a “Rolling Stone” magazine profile.  

"Look at that face,” he said. "Would anyone vote for that? Can you imagine that, the face of our next president?"

On Thursday, Trump argued that he was talking about Fiorina’s “persona,” not “her looks.”

Carson, Louisiana Gov. Bobby Jindal and Wisconsin Gov. Scott Walker have gone head-to-head with Trump with limited success.

“He’s a non-serious carnival act,” Jindal said Thursday. “Donald Trump is shallow. Has no understanding of policy. He’s full of bluster but has no substance. He lacks the intellectual curiosity to even learn.”

And after Trump repeatedly saying that he wants to build a wall along the entire southern U.S. border and have Mexico pay for it, Walker made a proposal to have a wall along the Canadian border that was largely dismissed.

Walker is now at 4.8 percent, and Jindal is at less than 1 percent, compared to Trump at 30 percent, according to the most recent averaging of polls by the nonpartisan website RealClearPolitics.

Meanwhile, Carson and former Florida Gov. Jeb Bush, the GOP’s establishment candidate and early presumptive frontrunner, have largely chosen to avoid the war of words with Trump, apparently taking the strategy that his campaign will eventually fizzle or implode in a fury of public backlash.

“I really should not have taken that bait,” Carson, who is running second in most national polls, also told Fox News on Friday night. “I just don’t want to get into that at all.”