The former US special envoy for Ukraine told House lawmakers on Thursday that he warned President Donald Trump’s personal lawyer Rudy Giuliani that the information he was receiving from Ukrainian political figures about former Vice President Joe Biden and his son was not credible, The Washington Post reported Thursday, citing two people familiar with his testimony.

Kurt Volker, who resigned one day after he was named in the release of a whistleblower report alleging Trump was using the power of the presidency to ask Ukraine to investigate the Bidens for political gain, said he attempted to warn Giuliani that his Ukrainian contacts — among them Ukraine’s former top prosecutor — weren’t trustworthy, the Post said, according to the people familiar.