In order to extol the virtues of the Caliphs in his debates with Shias while losing no opportunity to deny the merits of Ali ibn Abi Talib, Ibn Taymiyyah lost any sense of objective thinking, and employed a highly biased, flawed and intellectually dishonest approach. He went so far that he even attempted to deny the undeniable and authentic tradition of Ghadir, that no Sunni doubts is authentic. The well known Salafi scholar Al-Albani could not bring himself to remain silent over this, and after reading the shocking views of Ibn Taymiyyah, was compelled to write ‘at length’ over the issue.
ةٌمٌت نب ملسلا خٌش تٌأر ًننأ , ثٌدحلا نم لولا رطشلا فعض دق , امأ و رخلا رطشلا ,بذك هنأ معزف ! هعرست نم يرٌدقت ًف ةجتانلا هتغلابم نم اذه و اهٌف رظنلا ققدٌ و اهقرط عمجٌ نأ لبق ثٌداحلا فٌعضت ًف
Translation: When I saw Sheikh ul Islam Ibn Taymiyah considering the Hadith (For whosoever I am Mawla then Ali is his Mawla) as weak/doubtful in its first half and “lie in its second” then I had to write in length over this issue.In my viewpoint, the reason behind such exaggeration (of Ibn Taymiyah) was that he used to be hasty in deciding the inauthenticity of some Hadiths before seeing them properly (Silsilat ul Ahadith as-Sahiha, Volume No.4, Page No. 344)
We must ask what bias one would have to have against Ali ibn Abi Talib to go so far as to even deny the indisputable authenticity of Ghadir? This tradition is ubiquitous in books of Hadith, many of them having authentic chains, and so one can not claim he was not privy to this information given it ought to have been crystal clear. The excuse of being hasty if true is a terrible inditement on Ibn Taymiyyah and his scholarly rigour, but the reality is he was probably aware of this, but his bias clouded his judgement and ability to judge the tradition fairly.