Musnad Ahmad 31:98

Isma'il narrated to us, Hammam ibn Yahya informed us, from Zayd ibn Aslam, from 'Ata' ibn Yasar, from Abu Sa'id, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not write anything from me except the Quran. Whoever has written anything from me other than the Quran, let him erase it."