Musannaf Ibn Abi Shayba 3:6358

Waki’ narrated to us, he said: Sufyan narrated to us, from Ubayd al-Maktab, he said: Mujahid was asked about two men, one of whom recited Al-Baqarah, and the other recited Al-Baqarah and Al-Imran, and their bowing, prostration, and sitting were equal. Which of them is better? He said: "The one who recited Al-Baqarah." Then Mujahid recited: "And [it is] a Qur'an which We have separated [by intervals] that you might recite it to the people over a period, and We have sent it down progressively."