Musnad Ahmad 27:1221

Abu al-Nadr narrated to us, Abu Aqil—meaning Abdullah ibn Aqil—narrated to us, from al-Fadl ibn Yazid al-Thumali, Abu al-Ajlan al-Muharibi narrated to me, I heard Ibn Umar saying: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "Indeed, the tongue of the disbeliever will be dragged behind him on the Day of Resurrection for the distance of two farsakhs, and the people will trample upon it."