In his quest to win back estranged wife Khloe Kardashian, sources say Lamar Odom has promised not to drink again, but he doesn't appear to be holding his end of the bargain. Just months after overdosing in a Nevada brothel, Odom was spotted sipping liquor at a Los Angeles mall over the weekend.

The NBA champ, 36, was photographed using three $20 bills to pay for a cognac from a bar inside the Beverly Center on Mother's Day while friends were shopping. A source tells ET that Lamar "seemed happy" taking pictures with fans while there and had even visited the same bar earlier in the week.

Shortly after the photos were published Khloe tweeted, "Hummmmmm... People disappoint."

This slip-up isn't the first time Lamar's been seen drinking since his hospitalization. The former Los Angeles Laker was photographed at a bar in Sherman Oaks, California, over Easter weekend, where he ordered three Remy Martin drinks, according to TMZ. Lamar was reportedly at the bar until around 1 a.m., and went to church with Khloe and her family hours later.

WATCH: Lamar Odom Reveals He Wants to Remarry Khloe Kardashian

A source at the time told ET that Lamar "should not be consuming any alcohol right now, and was told that by his medical team."

"One thing is so clear -- Khloe would never get back with Lamar unless she knew 100 percent that he was maintaining his sobriety," the source stressed. "So him drinking again is a huge slap in her face."

In April, sources close to Khloe told ET that the 31-year-old reality star is expecting to move forward with her divorce from Lamar and would officially end their marriage "soon."

WATCH: Lamar Odom Bar Sighting Is 'Huge Slap' in Khloe Kardashian's Face

Khloe and Lamar married in 2009 after a month of dating and she originally filed for divorce in 2013, only to call if off following his drug overdose at the Love Ranch brothel in Crystal, Nevada, in October.

Part of Lamar's recovery was featured on Sunday's episode of Keeping Up With the Kardashians, which marked the first time he's been back on the show since his hospitalization. In the episode, Lamar seems to want to mend his broken marriage, but Khloe is reluctant about rekindling their relationship.

WATCH: Khloe Kardashian Will 'Soon' File for Divorce From Lamar Odom Again

"[Our marriage has] been a little tainted," she says in the episode. "We need to cut our ties, and we can figure it back out."

WATCH: EXCLUSIVE -- Kris Jenner Opens Up About Lamar Odom's Health, Hopes He and Khloe Kardashian Will Have a 'Happy Ending'

And a source close to Khloe has previously told ET she's sticking to that.

"Their divorce is still off," the source said. "She's still involved in all his medical decisions but he makes most of them on his own and is coherent enough to do so."

However, "Khloe still gets exasperated by the whole situation," the source added, "the fact that she's 31 years old and single, but still married and seeing her husband who she isn't together with every day, but she is being very patient and taking things day by day."