Musnad Ahmad 26:713

I read to my father: Ali ibn 'Asim narrated to you, Ibrahim al-Hajari narrated to us, from Abu al-Ahwas, from Abdullah ibn Mas'ud, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Beware of these two marked dice (ka'batayn) which are cast with a thud, for they are the gambling of the non-Arabs (Ajam)."