Musnad Ahmad 1034:193

Sufyan ibn 'Uyaynah narrated to us, from Mansur, from Ibrahim, from Hammam ibn al-Harith, who said: We were with Hudhayfah when a man passed by. They said: "This man conveys speech to the commanders." Hudhayfah said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "A qattat (slanderer/tale-bearer) will not enter Paradise."