Allah has commandedMuslims to be united, Unity is an obligation

MUSLIMS ARE ONE UMMAH
This nation of yours is one nation and I am your Lord, so worship
Me. Butthey disagreed and split into different sects. Each one will
return to Us. (Surat al-Anbiya', 92-93)
Hold fast to the rope of Allah all together, and do not separate.
Remember Allah's blessing to you when you were enemies and He
joined your hearts together so that you became brothers by His
blessing. You were on the very brink of a pit of the Fire and He
rescued you from it. In this way Allah makes His Signs clear to
you, so that hopefully you will be guided. (Surah Al 'Imran, 103)
The believers are brothers, so make peace between your brothers and
have fear of Allah so that hopefully you will gain mercy. (Surat
al-Hujurat, 10)
Obey Allah and His Messenger and do not quarrel among yourselves lest
you lose heart and your momentum disappear. And be steadfast. Allah
is with the steadfast. (Surat al-Anfal, 46)
ALLAH COMMANDS ALL MUSLIMS TO STRIVE TOGETHER AS ONE
What reason could you have for not fighting in the Way of Allah –
for those men, women and children who are oppressed and say, 'Our
Lord, take us out of this city whose inhabitants are wrongdoers!
Give us a protector from You! Give us a helper from You!' ? (Surat
an-Nisa', 75)
Struggle with them until there is no more corruption and the
religion is Allah's alone. If they stop, Allah sees what they do,
(Surat an-Anfal, 39)
…those who, when they are wronged, defend themselves. (Surat ash-Shura, 39)
Allah loves those who struggle in His Way in ranks like well-built
walls. (Surat as-Saff, 4)
MUSLIMS STRIVE TOGETHER AS ONE
There have been twelve months with Allah in the Book of Allah, from
the day He first created the heavens and earth. Four of them are
forbidden. That is the True Religion. So do not wrong one another
during them. However, STRUGGLE WITH THE IDOLATERS TOTALLY JUST AS
THEY STRUGGLE WITH YOU TOTALLY , and know that Allah is with those
who guard against evil. (Surat at-Tawba, 36)
MUSLIMS STRIVE TOGETHER UNDER THE LEADERSHIP OF THE IMAM
"Remember when you left your family early in the day TO INSTALL THE
BELIEVERS IN THEIR BATTLE STATIONS. Allah is All-Hearing,
All-Knowing". (Surah Al 'Imran: 121)
MANY A PROPHET HAS BEEN FOUGHT, WHEN THERE WERE MANY THOUSANDS WITH
HIM! They did not give up in the face of what assailed them in the
Way of Allah, nor did they weaken, nor did they yield. Allah loves
the steadfast. (Surah Al 'Imran, 146)
GO OUT TO FIGHT, LIGHT- ARMED AND HEAVY-ARMED, AND STRIVE WITH YOUR
WEALTH AND YOURSELVES IN THE WAY OF ALLAH. That is better for you if
you only knew. (Surat at-Tawba, 41)
O PROPHET. SPUR ON THE BELIEVERS TO FIGHT. If there are twenty of
you who are steadfast, they will overcome two hundred; and if there
are a hundred of you, they will overcome a thousand of the
unbelievers, because they do not understand. (Surat al-Anfal, 65-66)