6. `Abd Al-Wahid ibn Muhammad ibn `Abdus al-Naysaburi al-`Attar said in Naysabur year 352 AH that `Ali ibn Muhammad ibn Qutaybah al-Naysaburi said that I heard al-Fadl ibn Shadhan that

when I was present, a dualist asked Abu al-Hasan `Ali ibn Musa al-Rida : “I say: Verily, there are two producers of the Universe. Then what is the proof that He is One?” Consequently, he replied, “You statement: “Verily, He is two” is proof that He is One, because you have not claimed the second except after ascertaining the One. Therefore, One is agreed upon, and more than one is disagreed.