Sources tell TMZ ... the rapper was hired to perform at the Bar Mitzvah held by oil and gas entrepreneur Matt Pouldar, who spent a ton of money to give his first-born son, Shane, the celebration of his dreams.

Check out the vid ... Lil Baby performs surrounded by a hyped crowd, who raps almost every word alongside the A-lister.

The party, which was held at the Beverly Hills Hotel Saturday night, was a lavish affair ... where sources say Lil Baby was paid a high six figures to make a personal appearance. We're told the rapper's attendance was a top-secret surprise for Shane and the other attendees, which included the teen's family and friends.

Sources say CEO of DWE Talent Management David Weintraub was the go-to talent booker for this party and helped pull off the surprise ... and, boy, was it a good one. Even Drake's dad, Dennis Graham showed up to the bash.

Lil Baby isn't the first celebrity to accept a paycheck for a private gig, however. Remember, back in January 2021, Beyoncé took the stage at the opening of a new luxury hotel in Dubai ... where all phones were banned from the event.

Then, at the start of 2024, Rihanna reportedly brought home $6 million to perform at the wedding of one of billionaire Mukesh Ambani's sons.

Oh, and then there's famed tenor Andrea Bocelli ... who has performed at a number of celebrity weddings, including Kourtney Kardashian's, Princess Eugenie's, and Kim Kardashian's, to name a few.