Musannaf Ibn Abi Shayba 22:49

Ja'far ibn 'Awn narrated to us, he said: Ibrahim ibn Isma'il al-Ansari informed us, he said: Ibn Shihab informed us, from 'Ubayd ibn al-Sabbaq, that 'Uthman said: "It was only revealed in the tongue of Quraysh," meaning the Qur'an.