The Messenger of Allāh (Peace and Blessings of Allāh be upon him and his family) said:
“Loving ‘Alī is the sign of belief, and hating ‘Alī is the sign of hypocrisy.”
— Muslim, al-Tirmidhī, Ibn Mājah, Aḥmad, Tārīkh al-Kabīr (by Imām al-Bukhārī), Ḥilyat al-Awliyāʼ (by Abū Nuʻaym) and others.
This tradition of Prophet (Peace and Blessings of Allāh be upon him and his family) was popular to the extent that some of the Companions (may Allāh be well pleased with them all) used to say:
“We recognized the hypocrites by their hatred of ‘Alī.”
— Fadā’il al-Ṣaḥāba by Imām Aḥmad, al-Isti‘āb, by Ibn ‘Abd al-Barr and others.
It is also narrated by Muslim in his Ṣaḥīḥ that ‘Alī (may Allāh be well pleased with him) said:
“The Unlettered Prophet (Peace and Blessings of Allāh be upon him) informed me that none but a believer would love me and none but a hypocrite would hate me.”