Love of Ali
It was narrated that Ali (radi Allahu anhu) said: "The Unlettered Prophet (sal Allahu alaihi wa sallam) informed me that none but a believer would love me and none but a hypocrite would hate me." [Sahih Muslim]
Ali bin Abu Talib (radi Allahu anhu) was brought up under the careful patronage of the Prophet (sal Allahu alaihi wa sallam) and his venerable wife Khadeeja (radi Allahu anha). He was the first among children to accept Islam. He became the fourth khalifa of the Islamic state.
Unmatched are the feats performed by the senior Companions in the service and defence of Islam. That is why anyone who loves Islam loves and respects them, as their very presence was a thorn in the side of the enemies of Islam. Ali (radi Allahu anhu) is also one among such great Companions. Therefore, love for him is a sign of love of Islam, and enmity towards him is a sign of hypocrisy.
Love for Ali (radi Allahu anhu) does not mean going beyond all limits, which is a trait found in some of the innovators. Some of these innovators regard him sinless like prophets. Others hold him superior to Abu Bakr and Umar (radi Allahu anhum). Still others invest him with divine attributes, while some go still farther and deify him.
Differences among the Companions were due to differences in their judgement. Ahlus-Sunnah (people of the Prophet's path) consider it advisable to hold their tongues and avoid blaming any of them in such matters, as they are all superior to us.