The concept of loyalty and disavowal (al-wala’ wa’l-bara’) and its importance
Question

There are those who say that it was the Kharijites who came up with the phrase loyalty and disavowal (al-wala’ wa’l-bara’), and they used these exact words, but they did not interpret the phrase in a comprehensive way that included beliefs (‘aqeedah).
Praise be to Allah.Loyalty and disavowal (al-wala’ wa’l-bara’) is one of the basic principles of Tawheed (affirmation of the oneness of Allah)
Loyalty and disavowal (al-wala’ wa’l-bara’) is one of the basic principles of Tawheed and is proven in both wording and meaning
Allah, may He be exalted, says (interpretation of the meaning):
“O you who have believed, do not take the Jews and the Christians as allies. They are [in fact] allies of one another. And whoever is an ally to them among you - then indeed, he is [one] of them. Indeed, Allah guides not the wrongdoing people. 
So you see those in whose hearts is disease hastening into [association with] them, saying, ‘We are afraid a misfortune may strike us.’ But perhaps Allah will bring conquest or a decision from Him, and they will become, over what they have been concealing within themselves, regretful.
And those who believe will say, ‘Are these the ones who swore by Allah their strongest oaths that indeed they were with you?’ Their deeds have become worthless, and they have become losers.
O you who have believed, whoever of you should revert from his religion - Allah will bring forth [in place of them] a people He will love and who will love Him [who are] humble toward the believers, powerful against the disbelievers; they strive in the cause of Allah and do not fear the blame of a critic. That is the favor of Allah; He bestows it upon whom He wills. And Allah is all-Encompassing and Knowing 
Your ally is none but Allah and [therefore] His Messenger and those who have believed - those who establish prayer and give zakah, and they bow [in worship]. 
And whoever is an ally of Allah and His Messenger and those who have believed - indeed, the party of Allah - they will be the predominant”
[al-Ma’idah 5:51-56]
“And [mention, O Muhammad], when Abraham said to his father and his people, ‘Indeed, I am disassociated from that which you worship, 
Except for He who created me; and indeed, He will guide me’”
[az-Zukhruf 43:26-27]
“There has already been for you an excellent pattern in Abraham and those with him, when they said to their people, ‘Indeed, we are disassociated from you and from whatever you worship other than Allah . We have denied you, and there has appeared between us and you animosity and hatred forever until you believe in Allah alone’”
[al-Mumtahinah 60:4].
And there are other verses which speak of the obligation to take the believers as allies and friends, and prohibit taking the disbelievers as such, and speak of the obligation to disavow them and what they worship.
Ahmad (22132) narrated from Mu‘adh that he asked the Messenger of Allah (blessings and peace of Allah be upon him) about the best of faith, and he said: “The best of faith is to love for the sake of Allah and hate for the sake of Allah, and to keep your tongue busy in mentioning Him.” Shu‘ayb al-Arna’oot said: It is saheeh because of corroborating evidence.
At-Tabaraani narrated from Ibn ‘Abbas (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “The strongest bond of faith is taking believers as allies and friends for the sake of Allah and to regard disbelievers as enemies for the sake of Allah, to love for the sake of Allah and hate for the sake of Allah, may He be glorified and exalted.” Classed as saheeh by al-Albani in Saheeh al-Jaami‘ as-Sagheer, no. 2539.
The concept of loyalty and disavowal (al-wala’ wa’l-bara’)
Shaykh Ibn Baaz (may Allah have mercy on him) was asked: Please could you explain the concept of loyalty and disavowal (al-wala’ wa’l-bara’): to whom does it apply and is it permissible to take the disbelievers as allies and friends?
He replied: what is meant by loyalty and disavowal (al-wala’ wa’l-bara’) is loving the believers and taking them as allies and friends, and hating the disbelievers, regarding them as enemies and disavowing them and their religion. This is what is meant by loyalty and disavowal (al-wala’ wa’l-bara’), as Allah, may He be glorified, says in Soorat al-Mumtahinah (interpretation of the meaning):
“There has already been for you an excellent pattern in Abraham and those with him, when they said to their people, ‘Indeed, we are disassociated from you and from whatever you worship other than Allah . We have denied you, and there has appeared between us and you animosity and hatred forever until you believe in Allah alone’”
[al-Mumtahinah 60:4].
Hating them and regarding them as enemies does not mean that you should mistreat them or transgress against them if they are not in a state of war with the Muslims. Rather what it means is hating them in your heart and regarding them as enemies in your heart, and not taking them as friends. But you should not offend them, harm them or mistreat them. If they greet you, then return their greeting, advise them sincerely and direct them to do good, as Allah, may He be glorified and exalted, says (interpretation of the meaning):
“And do not argue with the People of the Scripture except in a way that is best, except for those who commit injustice among them”
[al-‘Ankaboot 29:46].
The People of the Scripture are the Jews and Christians, and other disbelievers who have been granted security, or have a peace treaty with the Muslims, or are living under Muslim rule. But whoever among them commits injustice is to be punished for his injustice and wrongdoing, otherwise what is prescribed for the believer is to argue with them in the way that is best, with both the Muslims and the disbelievers, whilst hating them for the sake of Allah, because of the verse quoted above.
End quote from Majmoo‘ Fataawa Ibn Baaz (5/246).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: What is loyalty and disavowal (al-wala’ wa’l-bara’)?
Answer: Disavowal and loyalty for the sake of Allah, may He be glorified, means that a person disavows everything that Allah disavowed, as He, may He be glorified and exalted) says (interpretation of the meaning):
“There has already been for you an excellent pattern in Abraham and those with him, when they said to their people, ‘Indeed, we are disassociated from you and from whatever you worship other than Allah . We have denied you, and there has appeared between us and you animosity and hatred forever’”
[al-Mumtahinah 60:4].
This is applicable with polytheists who associate others with Allah, as He, may He be exalted) says (interpretation of the meaning):
“And [it is] an announcement from Allah and His Messenger to the people on the day of the greater pilgrimage that Allah is disassociated from the disbelievers, and [so is] His Messenger”
[at-Tawbah 9:3].
So every believer must disavow every polytheist and disbeliever. This is with regard to people.
Similarly, the Muslim must disavow every deed that is not pleasing to Allah and His Messenger, even if it does not constitute disbelief, such as evildoing and sin, as Allah (may He be glorified, says (interpretation of the meaning):
“but Allah has endeared to you the faith and has made it pleasing in your hearts and has made hateful to you disbelief, defiance and disobedience. Those are the [rightly] guided”
[al-Hujuraat 49:7].
End quote from Fataawa Arkaan al-Islam, p. 183.
Shaykh Saalih al-Fawzaan (may Allah preserve him) said in Sharh Nawaqid al-Islam (p. 158): The Shaykh (may Allah have mercy on him) referred to one type of becoming allies with the disbelievers, which is supporting them, otherwise taking them as allies includes loving them in one’s heart, supporting them against the Muslims, praising them and so on, because Allah, may He be glorified and exalted, has commanded the Muslims to regard the disbelievers as enemies, hate them and disavow them. This is what is called, in Islam, loyalty and disavowal (al-wala’ wa’l-bara’). End quote.
The connection between the Kharijites and the phrase “loyalty and disavowal (al-wala’ wa’l-bara’)”
Connection between the Kharijites and the phrase “Loyalty and disavowal (al-wala’ wa’l-bara’)”
We do not know that the Kharijites had any particular view on the matter of loyalty and disavowal (al-wala’ wa’l-bara’), but those who go to extremes in labelling people as disbelievers (takfeer) in modern times may use this concept as an excuse for their extremism. This is due to a misunderstanding of this concept and what it implies, not because there is any problem with the concept itself.
And Allah knows best.