How to check if exist in the database with the laravel validator?

Suppose I am editing a post, when I submit the form I check if the post exists in the database with the id like below

$post = Post::where('id', '=', $request['post_id'] );
if ( $post ->exists() ) {
    // Update the post

But is there any way I can check with laravel validator? Right now my validation function looks like this.

$this->validate($request, [
    'post_id'          => 'required',
    'post_title'       => 'required',
    'post_content'     => 'required',

Yes, you can do that.

'post_id' => 'required|exists:posts,id'


'post_id' => 'required|exists:App\Models\Post,id'

When the form is submitted, it will check post_id exists in the posts table with the id column.