Is it permissible to cooperate with other Islamic groups?

The questioner : In the midst of many groups that call to Islam, it is observed that these groups have a strong bias toward their own parties; so we ask your Eminence to clarify...The Shaykh : ...whether it is permissible to cooperate with them? Knowing that if one does not cooperate with them, it will enable the communists and others, and if one cooperates with them, one will face bias, meaning a war against the Salafi methodology?

The Shaykh : We have spoken about this issue many times, and we say—if Allah wills—a brief word: It is not permissible for there to be multiple groups in the Muslim community, each group having a specific methodology and a specific leadership, where this leadership imposes its orders on its followers. This leads to an increase in division and disagreement among the Muslims, and it leads to making division a system followed among the Muslims. This is obviously contrary to the saying of the Lord of the Worlds: . And it was narrated in a hadith of Hudhayfah ibn al-Yaman (may Allah be pleased with him) in "Sahih al-Bukhari and Muslim" that he said: "The people used to ask the Messenger of Allah (peace and blessings be upon him) about good, and I used to ask him about evil, fearing that I might fall into it." So he asked him about many matters that concerned this noble Companion. He asked him, for example, about this good that they lived with the Prophet (peace and blessings be upon him); "Is there evil after him?" He answered that some of that will be, and after that there will also be good. He asked him again: "Is there evil after this good?" He said: . He continued the questions until he reached the point where he said (peace and blessings be upon him): , and do not be with a group from these groups unless they have an imam who is the imam of all the Muslims. If they have an imam, you must be with him. He said: So separate, and if not, separate from all those groups, even if you have to bite the trunk of a tree. This is the meaning of this hadith reported in "Sahih al-Bukhari and Muslim."
This means that it is not permissible for a Muslim to be biased toward one group over another. However, I say: It is incumbent upon the Islamic groups—and they have appeared on the scene, unfortunately!—that they all cooperate with one another, but on the condition that their cooperation is based on a correct foundation from the Book and the Sunnah and the methodology of the righteous Salaf. So if one refuses to cooperate with another group because it is not cooperating on this correct methodology of the Book and the Sunnah and what our righteous Salaf were upon, then in that case, cooperation is not recommended due to the contradiction of what the Messenger of Allah (peace and blessings be upon him) and his Companions after him were upon. So cooperation is obligatory, and division is forbidden. Whoever refuses but to divide, "Biraqsh has brought harm upon herself."