9:10 AM PT -- A source close to Keke Palmer tells us Darius Jackson made his way into her home that Sunday and began to cuss Keke out as she was on the phone with Sharon. We're told Sharon made the threat about the bullet because she feared for her daughter's safety and couldn't be there in person to protect Keke.

We've also obtained Sharon's response to the text message from Darius' mother.

Keke Palmer's ex, Darius Jackson, is denying her bombshell abuse allegations -- and is levying his own claims against her mother ... whom he insists threatened to put a bullet in his head.

Sources close to Darius tell TMZ the latest issue between the couple stems from an argument over the custody of their infant son, Leo. Per our sources ... Darius had texted Keke about going to pick up his son to watch football last Sunday -- but when he arrived to Keke's place, Leo wasn't there.

From there, an argument between Darius and Keke ensued, and at some point, Keke got her mom, Sharon, on the phone and put her on speaker -- and we're told Sharon was screaming/cussing Darius out. It was during that time when Sharon allegedly told Darius she'd put a bullet in his head ... which brought things to another level.

Darius then attempted to wrestle Keke's phone away from her -- which our sources say is what's depicted in one of KP's exhibits from her restraining order filing last week ... which shows them tussling and struggling on the couch.

We're told Darius absolutely denies abusing Keke ... and our sources say cops even came over and didn't find any probable cause to arrest him for DV. They didn't even file a report, we're told ... which our sources say backs up DJ's account.

We're told Darius' mother, Yhinyer, caught wind of the bullet to the head threat, and texted Sharon over it.

We should note, Keke also included screenshots from an altercation between her and Darius on the stairs from Feb. 2022 in her restraining order filing -- we don't know what led to that incident.

In any case, our sources say Darius is sticking to his story ... and that denies the recent allegations of abuse. A judge, of course, felt a temporary restraining order was warranted.

Keke was granted her TRO ... not to mention temporary sole custody of the child. A hearing on the matter is scheduled for Dec. 5 -- where Darius will be able to plead his case.

As we reported ... Keke was spotted out in public Saturday working on what appeared to be a shoot, and she had young Leo with her. She also received a rose bouquet from someone.