Question Summary:
Is it Kufr to assist the disbelievers against the Believers?

Question Detail:

Is it Kufr to assist the disbelievers against the Believers?
 
I just wanted to know to increase my knowledge. Many Ulama say it is Kufr by Ijma and the one who does support the kuffar against the Muslims is an Apostate.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh. 
Undoubtedly it is a great sin to assist the disbelievers against Muslims. Allah Ta’ala says in The Quran,
يَا أَيُّهَا الَّذِينَ آمَنُوا لَا تَتَّخِذُوا عَدُوِّي وَعَدُوَّكُمْ أَوْلِيَاءَ تُلْقُونَ إِلَيْهِم بِالْمَوَدَّةِ وَقَدْ كَفَرُوا بِمَا جَاءَكُم مِّنَ الْحَقِّ يُخْرِجُونَ الرَّسُولَ وَإِيَّاكُمْ ۙ أَن تُؤْمِنُوا بِاللَّهِ رَبِّكُمْ إِن كُنتُمْ خَرَجْتُمْ جِهَادًا فِي سَبِيلِي وَابْتِغَاءَ مَرْضَاتِي ۚ تُسِرُّونَ إِلَيْهِم بِالْمَوَدَّةِ وَأَنَا أَعْلَمُ بِمَا أَخْفَيْتُمْ وَمَا أَعْلَنتُمْ ۚ وَمَن يَفْعَلْهُ مِنكُمْ فَقَدْ ضَلَّ سَوَاءَ السَّبِيلِ
O you who believe! Take not My enemies and your enemies (i.e. disbelievers and polytheists, etc.) as friends, showing affection towards them, while they have disbelieved in what has come to you of the truth (i.e. Islamic Monotheism, this Quran, and Muhammad SAW), and have driven out the Messenger (Muhammad SAW) and yourselves (from your homeland) because you believe in Allah your Lord! If you have come forth to strive in My Cause and to seek My Good Pleasure, (then take not these disbelievers and polytheists, etc., as your friends). You show friendship to them in secret, while I am All-Aware of what you conceal and what you reveal. And whosoever of you (Muslims) does that, then indeed he has gone (far) astray, (away) from the Straight Path. (Al-Mumtaĥinah 1)
If a Muslim assists the disbelievers against the Muslims, and his intention is only for worldly gains (e.g. money), while his belief (Aqidah) remains correct, then it would not be considered as Kufr. [1]
If however the person assists the disbelievers against the Muslims because of his love for them (the disbelievers) and to support them against Muslims, then it would constitute Kufr.[2]    
 Making Takfeer of someone is indeed a very serious issue that results in serious consequences. Hence extreme care and precautions must be taken when issuing such rulings. Takfeer must only be assigned to trusted Ulama (scholars) who are fully aware of the principles and real meanings and indications of words. The great scholar, Allamah Ibn Abideen says in his Radd al-Muhtar: “The Fatwa of Kufr is not given to a Muslim when his words have the possibility of being interpreted in better (Hasan) manner (not amounting to Kufr)”.[3]
Extreme care and precaution in issuing Kufr was also the practice of the Sahabah and the pious predecessors. It is narrated in a Hadith,
ثنا الأعمش عن أبي سفيان قال أتينا جابر بن عبد الله وكان مجاورا بمكة وكان نازلا في بني فهر فسأله رجل فقال هل كنتم تدعون أحدا من أهل القبلة مشركا قال معاذ الله وفزع لذلك قال هل كنتم أظنه تدعونه كافرا قال لا
Narrated by al-A`mash, from Abu Sufyan: We came to see Jabir ibn `Abd Allah who lived in Makkah and resided with the Banu Fihr. A man asked him: "Did you [the Companions] use to call anyone from the People of the Qibla [i.e. Muslims], 'Mushrik'?" He replied: "I seek refuge in Allah." The man continued: "Did you call anyone from them 'Kafir'?" He said: "No." (Ibn Asakir in Tibyan al Kadhib al Muftari)
In another Hadith,
 
‏ ‏عن ‏ ‏أنس بن مالك ‏ ‏قال قال رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏ثلاث من ‏ ‏أصل ‏ ‏الإيمان ‏ ‏الكف ‏ ‏عمن قال لا إله إلا الله ولا نكفره بذنب ولا نخرجه من الإسلام بعمل والجهاد ماض منذ بعثني الله إلى أن يقاتل آخر أمتي ‏ ‏الدجال ‏ ‏لا يبطله ‏ ‏جور ‏ ‏جائر ‏ ‏ولا عدل عادل والإيمان بالأقدار
‏ Anas bin Malik (Radhiallahu Anhi) narrates from the Prophet (Peace be upon him) who said: Three things are the roots of faith (1) To refrain from (killing) a person who says “La ILaha IllalAllah” (2) Not to declare him an unbeliever whatever sin he commits (3) and also not to declare him out of Islam due to any of his deed. Jihad continues from the day I was sent as Prophet to the day that last member of my community fight with the Dajjal. The tyranny of any tyrant and the justice of any just (ruler) will not invalidate it. One must have faith in Divine Decree. [Sunnan Abu Dawud, Volume No. 2, Hadith # 2170]
 
And Allah Ta’āla Knows Best
Arshad Ali
Student Darul Iftaa
Trinidad
Checked and Approved by,
Mufti Ebrahim Desai.
http://www.daruliftaa.net/