THE BASIS OF RIGHT GUIDANCE
“The Religion of the Muslims is built upon following the Book of Allaah, the Sunnah of His Prophet (sallallaahu ‘alayhi wa sallam) and that which the Ummah has agreed upon. So these are the three infallible usool (fundamentals). So whatever the Ummah differs in, then it is referred back to Allaah and His Messenger. Thus, it is not for anyone to set up a person for the Ummah, and to call to his way and form walaa’ (love, loyalty and allegiance) and ‘adaa (enmity and hatred) based upon that, except for the Prophet (sallallaahu ‘alayhi wa sallam). Nor is any speech set up for them based upon which they form walaa’ and ‘adaa except for the Speech of Allaah, and that of His Messenger, and that which the Ummah has agreed upon. Rather, this is that practice of the people of innovation, who set up a person or a saying, with which they cause splits in the Ummah; forming walaa‘ and ‘adaa based upon that saying or ascription.” 
Imaam Ibn Taymiyyah – rahimahullaah – said:
“It is not upon anyone to ascribe himself to a particular Shaykh and to have walaa‘ with those who follow him, or to have ‘adaa based upon that. Rather, he should have walaa‘ for everyone from the people of eemaan (i.e. he is a Muslim) and is known to have taqwaa (piety and obedience to Allaah and that which He has ordered and prohibited), from the Shaykhs, or from others. No one should be particularised with an increase in walaa’, except if he sees in him greater eemaan and taqwaa. So precedence is given to those whom Allaah and His Messenger have given them to. Allaah the Exalted said:
“O Mankind! Indeed we created you from a man and a woman and made you into tribes and nations so that you may know one another. Indeed the most noble of you with Allaah are those that have the most taqwaa (piety)” [Sooratul Hujuraat 49:13] 
SECTARIANISM AND MISPLACED LOYALTIES
Shaykhul-Islaam Ibn Taymiyyah said:
“Indeed the people of the Sunnah do not follow anyone (unconditionally) other than the Messenger of Allaah (sallallaahu ‘alayhi wa sallam); who does not speak from desires, rather it is nothing less than Revelation sent down to him. So it is obligatory to affirm all that he informs, and to obey all that he commands. This status is not given to anyone else from this Ummah. Rather, everyone’s statement can be taken or left except for that of the Messenger of Allaah (sallallaahu ‘alayhi wa sallam). So whoever sets up an individual other than the Messenger of Allaah(sallallaahu ‘alayhi wa sallam); such that the one who loves and agrees with him is reckoned to be from Ahlus-Sunnah wal-Jamaa‘ah, and the one who differs with him is reckoned to be from the people of innovations and sectarianism – as happens with those groups who follow certain Imaams of kalaam (rhetorical speech) – then the person doing so is from the people of innovation, deviation and sectarianism.” 
He – rahimahullaah – further stated:
“Indeed many – from the people who say such things – follow their desires in this, in order to elevate their egos, or to gain leadership, or whatever is connected to it. Their intention is not to make the Word of Allaah uppermost, nor is it to make the Religion purely for Allaah. Indeed they have hatred for those who oppose them, even if it is a mujtahid (a scholar striving his utmost to arrive at the truth) who is excused and whom Allaah is not angry with. Likewise, they are pleased with those who agree with them – even if it is an ignorant person with evil intentions – who neither has any knowledge or good intent. This leads them to praise those who Allaah and His Messenger have not praise and to censure those whom Allaah and His Messenger have not censured. It also causes them to have walaa’ (love and allegiance) and ‘adaa (enmity and hatred) based upon their own self-desires and not upon the Religion of Allaah and His Messenger … So whoever does this will only bring about fitan (trials and tribulations) between the people.” 
PRESERVING LOVE AND UNITY
Shaykh ‘Abdul-‘Azeez Ibn Baaz (d.1420H) – rahimahullaah – said:
“The Religion of Allaah orders to judge (with justice) in all matters and not to have walaa’ (love, loyalty and allegiance) with your brother merely because he agrees with you, or to have ‘adaa (enmity and hatred) merely because he disagrees with you on a certain opinion or issue. This is not from justice at all! The Companions (radiyallaahu ‘anhum) differed in many issues, yet this did affect the overall happiness and sincerity between them, nor their walaa’ and love for each other – may Allaah be pleased with them all. So the Believer acts upon the Sharee‘ah (prescribed and divine Islaamic Law) of Allaah, follows the truth, gives precedence to the evidences before anyone – yet in doing so, he does not oppress his brother, nor negate doing justice to him when he differs regarding any issue of ijtihaad (personal reasoning) in which the evidences are not so apparent. Likewise is the case for those issues in which differences occur due to different interpretations of the text. So in such instances he is excused and it is upon you to sincerely advise him and to love only the good for him and not to split-up, nor to have enmity or hatred between you and your brother – and there is no might, nor power except with Allaah.” 
 Majmoo‘ul Fataawaa (20/164) of Ibn Taymiyyah.
 Majmoo‘ul Fataawaa (11/512).
 Majmoo‘ul Fataawaa (3/346-347).