I searched your posts and only found you claiming to have linked it, but never saw any link.
I think you're probably referring to a leaked phone call from a Russian crony between Biden and Poroshenko.
A phone call recording with former Vice President Joe Biden and former President of Ukraine Petro Poroshenko was leaked. Read the transcript here.
www.rev.com
This is probably what you're referring to:
And despite of the fact that we didn’t have any corruption charges, we don’t have any information about him doing something wrong, I especially asked him … No, it was the day before yesterday. I especially asked him to resign in his position as a state person, and despite of the fact that he has support in the public, and as a finish of my meeting with him, he promised me to give me the statement of his resignation, and one hour ago he bring me the written statement of his resignation.
Poroshenko hired Shokin because they were old guard corrupt cronies together. I have no doubt that Poroshenko wanted to keep his pet around.