Musnad Ahmad 1244:1

Bishr ibn al-Mufaddal narrated to us, he said: Abd al-Rahman ibn Ishaq narrated to us, from al-Zuhri, from Humayd ibn Abd al-Rahman, from his mother, Umm Kulthum, from the Prophet, may God bless him and grant him peace, that he said: "The liar is not the one who speaks to reconcile between people."