Assalam 'Alaykum wa Rahmatallahi ta'ala wa Barakatahu,
Bismillah wal Hamdulilah was Salatu was Salam 'ala Sayyidina Rasul Allah,
Indeed I have recieved the translation of Imam 'Abdul Kahir ibn Tahir al-Baghdadi's book "Al-Farq Baynul Firaq" or "Moslem Schisms and Sects"
The writer is from Ahlul Sunnah wal Jam'ah as illustrated by the introduction (he is Ashari). While although he says some things in here are kufr that I had not heard before (for example if you deny the consensus of the companions is a proof thats kufr) and I believe there is no ijm'a on - yet he does write what Syed Shaykh al-Ninowy said about Sayyidina Mu'awiyah (Radi Allahu 'Anhu). Therefore we cannot assume it is a new Ghumari-Ninowy position but in fact has roots in the history of Islam. This does not mean I agree with it however! I totally agree with Qadi Iyad's position on the companions which states we assume everything about them in a positive light! But this does mean that I want an explanation with this - as I thought this was a bid'ah stance not held by Ahlul Sunnah wal Jama'ah - not even a point of disagreement.
The exact wording insha Allah in the English translation are as follows from the chapter describing Ahlul Sunnah wal Jama'ah:
"They recognize the Imamate of 'Ali in its time. They judge 'Ali rightful in his wars in Basra, in Siffin, and in Nahrawan, and they assert that Talha and al-Zubair repented and withdrew from warfare against 'Ali but that al-Zubair was slain by 'Amr ibn Jurmuz in Wadi Siba' after his withdrawal from the battle. When Talha was about to leave, Merwan ibn al-Hakam who was with the Party of the Camel, shot him with an arrow and killed him. They say that '..'isha was aiming to set affaris right between the two parties but that Banu Dabba and al-Azd overruled her opinion and fought against 'Ali without her permission, so that the succeeding events occured. Regarding al-Siffin they rule that right was on the side of 'Ali, while Mu'awiyah and his supporters wronged him by means of an interpretation as a result of which they became sinners but not heretics. They declare that right was with 'Ali in arbitration, yet the two judged did not sin by depriving him of his office, which necessitated his dismissal, and by the deception which one of the two arbiters practised against the other."