Cassie's weighing in on Kanye West's recent pro-Diddy posts ... signaling the rapper should just keep his mouth shut about the whole situation.

The singer-songwriter reshared an IG post featuring Playboi Carti's response to Ye ... after Ye recently said he both he and Playboi "beat women" but they're not hated as much as Diddy is ... a post that pushed Carti to share "YE STFU."

Cassie doesn't add any of her own words to the post on her IG Story ... but, it looks like she's co-signing PC's message wholeheartedly.

Diddy was captured on video hitting Cassie multiple times in a hotel hallway in L.A. back in 2016 ... video CNN first shared last year has become the center of controversy in recent days after Diddy's attorney claimed the network destroyed the video.

As we've told you ... West has been showing a lot of public support for Diddy in recent days -- including sharing clips from a phone call with the music mogul while he's behind bars in MDC Brooklyn, a notorious federal detention center.

Of course, a collaboration between Kanye and Diddy -- the song "Lonely Roads Still Go to Sunshine," where some of their phone call plays as the intro -- may end up causing Ye some difficult personal problems.

As we told you, our sources say Kim Kardashian's considering asking a judge to strip Kanye of joint legal custody after the song's release ... since their attorneys had previously agreed any version of the song that was released wouldn't feature the ex-spouses' daughter North.

Ye broke that promise and put her on the track with Diddy, Diddy's son Christian "King" Combs, and a singer named Jasmine Williams.