I’m guessing the single source is me, because I speculated on here yesterday:
“It’s quite possible that the only reason Kennedy retired when he did was a gentlemen’s agreement he made with President Trump that the president would appoint Kavanaugh, who is Kennedy’s former clerk and friend.”
That’s about as solid sourcing as most of their fake news!
It's also just as possible that President Trump, while performing due diligence on his list of nominees, consulted with Justice Kennedy about Kavanaugh, told Kennedy that he was at the top of his list, and Kennedy then felt comfortable about announcing his retirement after that discussion.