It concerns the knowledge of what has been received regarding the prohibition of practicing dissimulation (taqiyyah) among the believers, and in seclusion and solitude. His very name serves as a witness for its narrator, let alone what he reported in it, saying:

Al-Mufaddal ibn Umar narrated: I entered upon my Master [Imam] al-Sadiq—peace be upon him—and he said:

"O Mufaddal, beware of establishing anything of Dhāt al-Radā (The Essence of Ruin)!"

I said: "May I be your ransom, what is Dhāt al-Radā?"

He said:

"These Opposites (al-ḍudūd)."

I asked: "And what are these Opposites?"

He said:

"Fasting, prayer, pilgrimage, or jihad. Whoever establishes them as a matter of religious profession has taken another god besides God."

Then he said:

"The one who establishes them in secret is like the one who leaves them in public, and the one who leaves them in public is like the one who establishes them in secret."

Abu Abd Allah al-Husayn bin Harun al-Sa’igh narrated in some of his writings, tracing the chain back to al-Mufaddal ibn Umar, who said: