Musnad Ahmad 1034:127

'Abd al-Rahman and Abu Nu'aym narrated to us, they said: Sufyan narrated to us, from Mansur, from Ibrahim, from Hammam ibn al-Harith, who said: We were with Hudhayfah, and it was said to him: "Indeed, so-and-so is reporting hadiths to Uthman." He 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."