Al-Wala' Wa'l-Bara' :
According to the 'Aqeedah of the Salaf (Parts 1,2&3)
By Muhammad Saeed al-Qahtaani
Publisher: Al Firdous Publications Ltd. (UK)
 Paperback  Volumes 1(123 Pages) 2 (240 Pages) & 3 (173 Pages)- 3 Volumes Full Set 

Description from the publisher:

This book was originally submitted in the form of a thesis for Master’s Degree to the Department of ‘Aqeedah of Umm al-Qorah University in Makkah, Saudi Arabia.

It is impossible to provide a literal translation in English of the words al-wala’ wa’ l-bara’, but the meaning of this Arabic term indicates, on the one hand, drawing near to what is pleasing to Allah and his Messenger and, on the other hand, withdrawing from what is displeasing to Allah and His Messenger, may Allah and His Messenger, may Allah bless him and grant him peace.

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Love is the source of wala' and hate is the source of bara'; it is by this that both the heart and the hand are moved to act. Wala' inspires intimacy, concern and help. Bara' provokes obstruction, enmity and rejection. Wala' and Bara' are both related to the declaration of faith and constitute essential elements in it. The evidence of this from the Qur'an and the Sunnah is considerable.

'Say, (O Muhammad, to mankind), If you love Allah, follow me; Allah will love you and forgive you your wrong actions. Allah is Forgiving, Compassionate. Say, Obey Allah and the Messenger. And If they turn away, then surely Allah does not love the disbelievers.'
{TM Qur'an  3:31-32}

'Whoever says, There is no god but Allah, and denies whatever he used to worship beside Allah, will find that his life and his property are protected, and his reward is with Allah.'
Sahih Muslim

'Let not the believers take disbelievers for their friends in preference to believers. Whoever does this has no connection with Allah unless you are guarding yourselves against them as a precaution. Allah bids you to beware (only) of Himself. And to Allah is the journeying.' 
{TM Qur'an 3:28}