This is well proven hadith in Sunni School of Thought. This is mentioned in Sahih Muslim and other books of hadith that Loving Imam Ali(as) is the symbol of faith and hating Imam is a sign of hypocrisy.
Sayyidina Ali (RA) narrated: Indeed, the Prophet (SAW) the unlettered Prophet asserted to me, “None will love you except a believer and none will despise you but a hypocrite.” Adi ibn Thabit said, “I belong to the generation for whom the Prophet (SAW) prayed.”
This is graded Hassan Sahih Hadith
Here is another translation
Sayyidina Abu Sa’eed al-Khudri (RA) said, “We the company of Ansar recognise the hypocrites by their jealousy for Ali ibn Abu Talib (RA) This hadith is gharib. Shu’bah questioned Abu Harun Abdi’s veracity. This is reported from A’mash, from Abu Saith, from Abu Sa’eed (RA)