مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4280
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah said: They used to recite behind the Prophet (ﷺ) and he said: "You made me confused in reciting the Qur'an."
Musnad Ahmad 4309lts isnad is hasan]