In the first place, it should be borne in mind that Islam is the religion of unity. It commands all those who want to work for Islam to unify their efforts and hold together for the noble cause of Da`wah (Islamic Call). In the Qur’an, Almighty Allah directs us saying: “And hold fast by the covenant of Allah all together and be not disunited, and remember the favor of Allah on you when you were enemies, then He united your hearts so by His favor you became brethren; and you were on the brink of a pit of fire, then He
saved you from it, thus does Allah make clear to you His communications that you may follow the right way.”
(Al-`Imran: 103)

Coming to the question in point, here is the fatwa issued by the well-known Muslim scholar Sheikh Yusuf Al-Qaradawi in this regard: “It is incumbent upon every Muslim to spare no pains in serving his religion; he should stand up for its issues, work for the enforcement of its laws, liberate its occupied territories, unify the efforts of Muslims in resisting the aggression. Such noble goals can by no means achieved individually; therefore, Muslims should melt their efforts in one crucible and act in unison. The Qur’an commands us to help one another in matters of obedience. Almighty Allah says:“Help ye one another unto righteousness and pious duty.” (Al-Ma’idah : 2). The Prophet, peace and blessings be upon him, is reported to have said: “Allah’s help lies with the community.”

The above-mentioned Islamic rule “what is needed for the fulfillment of an obligation is itself an obligation’ is correct. It underlines the fact that enemies of Islam are working together in a unified efforts to wage war against this religion of truth. Accordingly, Muslims are required to ally together, working in group to face this aggression. However, if members of the various groups become at odds, one should work individually or with other people not affiliated to a certain group; but he should not undermine the foundation of the group to which one is affiliated.”

Shedding more light on the issue of collective work, Sheikh `Abdur-Rahman `Abdul-Khaliq, a prominent Muslim scholar, states the following: “It should be noted that there is no Qur’anic authority nor evidence from the Sunnah that stands against the establishment of a group or the carrying out of collective work. On the contrary, all religious proofs call for collective Jihad, collective work for the benefit of the religion, the promotion of the work of Da`wah (Islamic Call) and making the banner of Islam flutter high in the breeze.

However, there are certain criteria to be observed in every group working in the field of Da`wah. These criteria may include the following:

1-Sticking to truth: The first thing to be borne in mind is that a Muslim should stick to truth in all cases. To achieve this, it’s important for a Muslim to follow the teachings of the Qur’an and Sunnah in all matters. He should let sincerity be a driving force that directs him in his quest for truth, dedicating all his work for attaining Almighty Allah’s Pleasure.

2- He is not allowed to declare dissention from the Muslim community nor open attack on them. One is not allowed under any condition to rebel against the whole Muslim Ummah or direct his weapons towards his Muslim brothers.”