Muhammad Ibn Muhammad Al-Mufid writes:

فأما الوحي من الله تعالى إلى نبيه صلى الله عليه وآله وسلم فقد كان تارة بإسماعه الكلام من غير واسطة وتارة بإسماعه الكلام على ألسن الملائكة والذي ذكره أبو جعفر رحمه الله من اللوح والقلم وما ثبت فيه فقد جاء به حديث، إلا أنا لا نعزم على القول به ولا نقطع على الله بصحته ولا نشهد منه إلا بما علمناه وليس الخبر به متواترا يقطع العذر ولا عليه إجماع ولا نطق به القرآن ولا ثبت عن حجة الله تعالى فينقاد له والوجه أن نقف فيه ونجوزه ولا نقطع به ولا نجزم له ونجعله في حيز الممكن فأما قطع أبي جعفر به وعلمه على اعتقاده فهو يستند إلى ضرب من التقليد ولسنا من التقليد في شئ

“What the revelation from God to Muhammad (s. ) is concerned, it was by hearing the words without any means and by hearing the words through the tongues of the angels, and as for what Abu Ja’far (As-Saduq) said about the tablet and the pen and confirmed about it, that a saying (Hadith) has been transmitted in this regard, but we do not firmly agree with it and do not have any certainty before God as to whether it is right and do not testify to anything except what we have gained knowledge about. Neither is the report about it continuously available (Mutawatir), which would justify a certainty, nor is there a consensus about it (Ijma’), nor does the Qur’an lose a word about it, nor was it confirmed by a proof of God that would support it. Thus, the apt way of dealing with it is that we stop at it and consider it conceivable but do not have any certainty and security about it and place it in the realm of the possible and as for the certainty of Abu Ja’far (As-Saduq) and his expression of faith in it, it is based on a blow of imitation (taqlid) and we have nothing to do with imitation (taqlid).” [Tashih-ul-I’tiqadat, page 122]

Comment:

If it were true that imitation (taqlid) means to follow an expert (marja’) in legal matters, then the revelation of the Prophet (s.) would be a legal matter and As-Saduq would be an ordinary layman and follower of an expert (marja’) in legal matters and al-Mufid has nothing to do with a concept that is now declared a God-imposed duty (Wajib). Either all this is correct or one finally admits that the concept alone is no proof of the concept that one puts in the mouth of the imams (a.) in order to keep the masses following the clerics at bay.