A. I have only quoted few orientalists, but also shown it from authentic ShiaH and Sunni books, the role of 'Abdullah ibn Saba. Usually the orientalists favor Shiahism and if 'Abdullah ibn Saba was a fairy tale, so many of the orientalists would not have mentioned him. Even a blind person can't deny the role Ibn Saba played in the origins of Shiahism.
B. The quote of 'Allamah ibn Khuldoon was taken from Shia'hs and Shiahism, there Genesis and Evolution, by Allamah Ehsan Elahi Zahir Shahid. He was the author of many books on Shiahs and their history, and later on he was killed by the Shias and was burred in Madinah. Also its mentioned in 'Abdullah ibn Saba, Tarikh kay Aiyne Main, by Hakim Faiz Alam Siddiqui. Shah Abdul 'Aziz Dahlawi (may Allah have mercy on him) has also written in details about Ibn Saba in his magnum opus called Tuhfa Ithna Ashariyyah.
And to add to the above list:
22. And it is narrated from Imam Abu Hanifah (may Allah have mercy on him),
"hAbdullah ibn Saba was a Jewish and he [supposedly] accepted Islam during the time of Sayyiduna 'Usman (may Allah have mercy on him) and he urged the people of Egypt to kill 'Usman (may Allah have mercy on him) and he would show much love for 'Ali (may Allah have mercy on him). He was a khabis from inside and his only mission was to create fitnah among the Muslims." (Musnad Imam-i-A'zam, p.158)
عبد اللّه بن سبا كان يهوديا فاسلم ايام عثمان وهوالذى حمل اهل مصر على قتل عثمان واظهر
الميل الى على وكان خبيث الباطن غرض الفساد بين المسلمين
23. Shaykh Abdul Qadir Jaylani (may Allah have mercy on him) says in Ghunyat al-Talibin,
"Sabain sect are attributed towards 'Abdullah ibn Saba and they said 'Ali is alive and will come back before Qiyamat."
واما لسبائية فمنسوبة الى عبداللّه بن سبا من دعوهم ان عليا لم يمت وانه يرجع قبل يوم القيامة