Musannaf Ibn Abi Shayba 22:221

Hussain bin Ali narrated to us, from Ibn Uyaynah, from Dawud bin Shabur, from Mujahid, who said: I used to judge people by their memorization of the Quran, until I prayed behind Maslamah bin Mukhallad. He began [reciting] Al-Baqarah, and he did not make a mistake in it, neither in a 'waw' nor in an 'alif'.