Musannaf Ibn Abi Shaybah 3807 — Those who permitted reciting behind

Yahya bin Abi Ishaq said: "I prayed Maghrib behind al-Hakam bin Ayyub. Abu al-Malih was standing beside Ibn Usamah. I heard Abu al-Malih reciting Surah al-Fatihah. When the imam said the salam, I asked Abu al-Malih: 'Were you reciting behind the imam while the imam was also reciting?' He said: 'Did you hear something?' I said: 'Yes.' He said: 'Yes, I was reciting.'"