Kitāb al-Ghayba > Refutation of all sects, which believed in Imamate of someone other than Master of the Age (a.s)
Hadith #7

وأما القائلون بإمامة عبد الله بن جعفر من الفطحية وجعفر بن علي، فقولهم باطل بما دللنا عليه من وجوب عصمة الإمام وهما لم يكونا معصومين، وأفعالهما الظاهر التي تنافي العصمة معروفة، نقلها العلماء،وهي موجودة في الكتب فلا نطول بذكرها الكتاب. على أن المشهور الذي لا مرية فيه بين الطائفة أن الإمامة لا تكون في أخوين بعد الحسن والحسين عليهما السلام. فالقول بإمامة جعفر بعد أخيه الحسن يبطل بذلك.

As for believers in Imamate of Abdullah Ibn Ja’far, namely the Fatahiyya, and that of Ja’far Ibn Ali, their creed is wrong, because an Imam has to be infallible and these two were not. Their evident actions, which contradict infallibility, are widely known and scholars have narrated them and they are present in books and we will not prolong the discourse by quoting them here. Besides, the established principle, which is beyond doubt amongst the Shia, is that Imamate shall not pass from one brother to another, after Hasan and Husain (a.s). Therefore, the Imamate of Ja’far, after his brother, is void.