Today we have something fun to play with
You all know the narrations that contain the ancient Shia belief of “al-Bada'”, for example:
ما بدا لله في شيء كما بدا له في إسماعيل ابني
Imam al-Sadiq says: “It hasn’t appear to Allah in anything as it appeared to him in my son Isma`il.”
Meaning that it would appear to Allah that Isma`il was the next Imam, then after Isma`il died in his father’s life, Allah (astaghfirullah) made the Imam his brother Musa instead, in other words he changed his mind as if he apparently never knew that the first one was going to die.To make a long story short, the Shia at the time fabricated these narrations as excuses to switch from following one Imam to the next, and so that they wouldn’t appear as liars in front of their followers.
Now the Twelver Shia scholar al-Saduq does like this narration, so he refutes it in his book “Kamal ul-Deen wa Tamam ul-Ni`mah” pg.69:
ما ذلك الخبر؟ ومن رواه؟ ومن تلقّاه بالقبول؟ فلم يجدوا إلى ذلك سبيلاً ، وإنّما هذه حكاية ولّدها قوم قالوا بامامة إسماعيل ، ليس لها أصلٌ
[What is this narration? who narrated it? who accepted it? they couldn’t answer, this is only a story made up by some folks who believed in the Imamah of Isma`il, it is baseless.]
Then he makes Takfir on those who believe in it by saying:
وعندنا من زعم أنَّ الله عزَّ وجلَّ يبدو له اليوم في شيء لم يعلمه أمس فهو كافرٌ والبراءة منه واجبة
[We believe that whoever states that something can be revealed to Allah today that he didn’t know yesterday is a Kafir, and it is a duty to be free from him.]
Now we’ll reveal to him what he didn’t know, Bismillah:
رواه سعد بن عبد الله الأشعري قال: حدثني أبو هاشم داود بن القاسم الجعفري قال: كنت عند أبي الحسن عليه السلام وقت وفاة ابنه أبي جعفر – وقد كان أشار إليه ودل عليه – فإني لافكر في نفسي وأقول: هذه قضية أبي إبراهيم وقضية إسماعيل، فأقبل علي أبو الحسن عليه السلام فقال: نعم يا أبا هاشم بدا لله تعالى في أبي جعفر وصير مكانه أبا محمد، كما بدا لله في إسماعيل بعدما دل عليه أبو عبد الله عليه السلام ونصبه، وهو كما حدثت به نفسك وإن كره المبطلون، أبو محمد ابني الخلف من بعدي عنده ما تحتاجون إليه ومعه آلة الإمامة والحمد لله
Sa`d bin `Abdullah al-‘Ash`ari said: abu Hashim Dawoud bin al-Qassim al-Ja`fari said: I was with Imam abu al-Hassan (as) when his son abu Ja`far died -and he had pointed to him and appointed him- So I started thinking to myself: “This is similar to the case of Imam abu Ibrahim (as) and Isma`il.” so abu al-Hassan (as) came to me and said: “Yes O abu Hashim, it appeared to Allah in abu Ja`far and he replaced him with abu Muhammad, it also appeared to Allah in Isma`il after his father abu `Abdullah had pointed to him and appointed him, it is exactly as you thought to yourself even if the haters will hate. abu Muhammad my son is my successor after me, he has what you need and the Imamah praise be to Allah.”
Source: Ghaybat al-Tusi, page 200.
In other words, al-Saduq is clueless because this is an authentic Shia narration with a chain of trustworthy Imami Shia, No Isma`ilis, No Zaydis.
Also it turns out this happened twice, not just with Isma`il and Musa, but it also happened with the children of `Ali al-Hadi, Muhammad and Hasan.
al-Bada’ x 2