مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4224
Musnad of Abdullah bin Mas'ood
It was narrated that Fulfulah al-Ju’fi said: I was among those who panicked and rushed to ‘Abdullah concerning the Mushafs. We entered upon him and a man among the people said. We have not come to visit you; rather we came when we got alarmed about this news. He said: The Qur'an was revealed to your Prophet (ﷺ) from seven gates with seven modes of recitation, and the Book before him was revealed from one gate and with one mode of recitation.
Musnad Ahmad 4252Its isnad is da’eef]