If there was any doubt about the staying power of Al Green’s 1971 single “Let’s Stay Together,” it vanished when President Barack Obama crooned a snippet of the song at a fundraiser in January.

Green, who was Obama’s opening act that night, never saw the president’s impromptu performance coming.

“We were all shocked,” Green says. “I wish he’d sang the whole song. He sounded better than me!”

It sparked a surge in downloads of “Let’s Stay Together.” Sales increased 490 percent in the week following the fundraiser, according to Billboard.

As shocked as he was, Green is accustomed to having other artists interpret his work. Before Obama, Tina Turner covered “Let’s Stay Together,” and Talking Heads’ version of “Take Me to the River” is as famous as the original. Green, 66, is also no stranger to sampling: His music has been used in countless hip-hop and R&B songs.

Green, an ordained pastor, says he usually listens to a song before signing off on a sample, but with some rap songs, he has a hard time understanding the appeal. “I don’t mean to slap rap music in the face,” Green says, “but I really am from the old school.”

Recently, Green’s teenager asked him if a particular song reflected reality.

“He said, ‘Hey Dad, is that real? The guy with all the money in his hand and a Jack Daniels in the other hand and all the girls in the shorts in the club?’ ” Green recalls. “I said, ‘If you don’t have money and you don’t have the Jack Daniels, the girls will be gone.’ ”

Green doesn’t reject hip-hop wholesale. His last studio album, 2008’s “Lay It Down,” was co-produced by Ahmir “Questlove” Thompson and James Poyser, both members of the Roots. It was his highest-charting album in 35 years. As a result, he hit the road hard, which is why it’s taken so long for a follow-up.

Green has recorded a few songs for his next record but probably won’t log any serious studio time until October. From there, things could take a while.

“I like to live with the song,” Green says. “I like to sleep with the song. I like to caress the song. I like to hug the song — well, I don’t want to go too far, but I like to know the song. You got to get to know the song before you can really talk about doing something with it.”

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