Hawzah News Agency ­– Love of the Prophet's family is stressed both in the Qur'an and the Sunnah. The Qur'an says:
 

Say; I ask of you no reward for this, save love for the kinsfolk (al-mawadda
fi’l-qurba). (Sura al-Shura, XLII:23)
 

The reference of the Arabic qurbå here is to those 'close' to the Prophet, as is evidenced by the fact that it is the Prophet himself who is making this request.

Loving his noble family, in addition to being a great honour, is a cause of remaining always in their proximity, emulating them in their exemplary virtues and their remoteness from any vice. In certain mutawatir hadiths, it is related that love of the Prophet's ahl al-bayt (Household) is a sign of faith, and enmity towards them a sign of faithlessness and hypocrisy. Whoso loves them, loves the Prophet and God, and whoso opposes them, opposes God and His Prophet.

In principle, loving the family of the Prophet is one of the obligations of the faith of Islam, about which there is no doubt or confusion; and all Muslims are at one as regards this principle, except for one group, known as the Nawasib, who are, for this very reason, regarded as having left the faith of Islam.

Reference:

Ayatollah Jafar Sobhani, Doctrines of Shii Islam, A Compendium of Imami Beliefs and Practices, Translated and Edited by Reza Shah-Kazemi, published by I.B.Tauris Publishers, London • New York  2003.