Shaykh ul-Islam (May Allah have Mercy on him):

And the  innovation (bid’ah)  of the Rāfiḍa is more severe than the innovation  of the Khawaarij. They accuse Abu Bakr and Umar of disbelief, and lie against the Prophet (ﷺ) and the Companions, in a manner that no one has brought the likes of, whilst the Khawaarij do not lie but the Khawaarij used to be more truthful and more courageous than them and more trustworthy in fulfilling their pacts than them and so fought more than them and they (the Rāfiḍa) are the most lying, the most cowardly, most deceitful and most lowly (of people) and they seek help from the disbelievers against the Muslims.  Indeed we have seen and the Muslims have seen that if the Muslims are tried with the disbelieving enemy, they (the Rāfiḍa) are with them (the disbelieving enemy) as was the case with Genghis Khan the disbelieving emperor of the Tatars.  For indeed the Rāfiḍa supported him against the Muslims.

Source: Methodology of the Prophetic Sunnah, vol 5, pg 154-155

Translated by Abu Yusuf Khaleefah
16th of Safar, 1438 AH (11-16-2016)
Masjid Nur Allah, Queens, NYC

Original Arabic

قال شيخ الإسلام (رحمه الله) والرافضة أشد بدعة من الخوارج وهم يكفرون من لم تكن الخوارج تكفره كأبى بكر وعمر ويكذبون على النبي صلى الله عليه وسلم والصحابة كذبا ما كذب أحد مثله والخوارج لا يكذبون لكن الخوارج كانوا أصدق وأشجع منهم وأوفى بالعهد منهم فكانوا أكثر قتالا منهم وهؤلاء أكذب وأجبن وأغدر وأذل وهم يستعينون بالكفار على المسلمين فقد رأينا ورأى المسلمون أنه إذا ابتلي المسلمون بعدو كافر كانوا معه على المسلمين كما جرى لجنكزخان ملك التتر الكفار فإن الرافضة أعانته على المسلمين [منهج السنة ج٥ ص١٥٤ -١٥٥]