Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said in al-Tis’eeniyyah (1/125): The sons of Adam cannot live in this world unless they help one another in word and deed.
Allah has created man weak and he needs to cooperate continuously with others throughout his life. This is clear in worldly affairs. To sum up, people cannot live unless they cooperate with one another.
The Muslims need one another with regard to both worldly and religious affairs, hence cooperation among Muslims is something important that Allah has enjoined and He has made cooperation the basis for religious and worldly well being. The Muslims – if they achieve this cooperation – are described as a strong, integrated structure, and as a single body. All of that confirms that cooperation and mutual support among them is something essential. That includes many aspects in the lives of Muslims, which are summed up in the words birr (righteousness) and taqwa (piety), as Allah says (interpretation of the meaning): “Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment” [al-Maa’idah 5:2]. These are two words that sum up all the attributes of goodness, such as belief, conduct, rulings and so on. Allah says, explaining the meaning of birr (righteousness) (interpretation of the meaning):
“It is not Al-Birr (piety, righteousness, and each and every act of obedience to Allah) that you turn your faces towards east and (or) west (in prayers); but Al-Birr is (the quality of) the one who believes in Allah, the Last Day, the Angels, the Book, the Prophets and gives his wealth, in spite of love for it, to the kinsfolk, to the orphans, and to Al-Masaakeen (the poor), and to the wayfarer, and to those who ask, and to set slaves free, performs As-Salaah (Iqaamat-as-Salaah), and gives the Zakât, and who fulfil their covenant when they make it, and who are patient in extreme poverty and ailment (disease) and at the time of fighting (during the battles). Such are the people of the truth and they are Al‑Muttaqoon (the pious)” [al-Baqarah 2:177]
Shaykh Ibn Baaz said in his Fataawa (200, 201): Among the things that are mentioned in the ahaadeeth about solidarity as enjoined in Islam, which means cooperating in righteousness and piety, are the words of the Prophet (peace and blessings of Allah be upon him): “Religion is sincerity” They said, “To whom, O Messenger of Allah?” He said, “To Allah and to His Book, to His Messenger, and to the leaders of the Muslims and their common folk.” Narrated by Muslim in his Saheeh. And he (peace and blessings of Allah be upon him) said: “The relationship between one believer and another is like a structure, parts of which support other parts,” and he interlaced his fingers. Agreed upon. And he (peace and blessings of Allah be upon him) said: “The likeness of the believers in their mutual love, mercy and compassion is that of the body; if one part of it complains, the rest of the body joins it in staying awake and suffering fever.” Narrated by al-Bukhaari and Muslim in their Saheehs.
These ahaadeeth and others like them clearly indicate that mutual support, compassion and care among Muslims, and cooperation in doing good, are obligatory. Likening them to a single structure or a single body indicates that by supporting and helping one another and showing compassion to one another, they will become united and integrated, and they will be saved from the evil of their enemies.
Allah says (interpretation of the meaning): “Let there arise out of you a group of people inviting to all that is good (Islam), enjoining Al-Ma‘roof (i.e. Islamic Monotheism and all that Islam orders one to do) and forbidding Al-Munkar (polytheism and disbelief and all that Islam has forbidden). And it is they who are the successful” [Aal ‘Imraan 3:104]
The leader of them all in this call and their example on this path is their Prophet and greatest leader, our Prophet Muhammad the Messenger of Allah (peace and blessings of Allah be upon him). He was the first one to call this ummah to affirm the Oneness of its Lord (Tawheed) and hold fast to His rope, and to unite in truth and form a single rank against the common enemy and to achieve its interests and serve its just causes, in accordance with the words of Allah (interpretation of the meaning): “Invite (mankind, O Muhammad صلى الله عليه وسلم) to the way of your Lord (i.e. Islam) with wisdom (i.e. with the Divine Revelation and the Qur’an) and fair preaching, and argue with them in a way that is better” [al-Nahl 16:125]
This straight path was also followed by his noble Companions and those who followed them in truth (may Allah be pleased with them all), and they attained the ultimate success, and Allah granted them the honor and victory that He had promised them.