وَتَعَاوَنُوا عَلَى الْبِرِّ وَالتَّقْوَىٰ ۖ وَلَا تَعَاوَنُوا عَلَى الْإِثْمِ وَالْعُدْوَانِ
Wata‘aawanoo ‘alal-birri wat-taqwaa. Walaa ta‘aawanoo ‘alal-ithmi wal-‘udwaan
(O you who believe) . . . help one another in piety and goodness and do not help one another in sin and aggression Suratul Mai’dah (No. 5), Ayat 2
Islam encourages its followers to work together for the common good, and to refrain from working together in matters that are inappropriate and unseemly. When believers work together there is motivation, enthusiasm and a rise in spirit. Each believer is encouraged by the response of the other, and in this way a spark of goodness can become a great [positive] fire. The fire then engulfs society and the members are spurned towards good actions.
Cooperating with others must be for the sake of Allah only. Thus there would not be expectations of praise, or reward, or reciprocal favors. This makes it easier for people to work together without being disillusioned or discouraged.
There can be no cooperation in wrong actions, even if it is with close friends or family members. The only way to discourage evil from spreading in society is when people do not work together for it, refuse to help one another and through that show their disapproval of the action. This will in turn diminish the rise of such evils in society. To support wrong in any way, is to allow the wrong to happen. A Hadith of the Holy Prophet (s) says: On the Day of Judgment a caller will call out; where is the oppressor, and the helpers of the oppressor and those who made themselves like the oppressors? . . . until even those will be called who prepared a pen for the oppressor, or who filled the inkpot for them. Then they will all be placed in a coffin made of iron and thrown into the Hell-fire.
Communities can grow and progress when people follow the above verse. Good in the community will increase, and evil will decrease. What can be achieved through unity of action cannot be achieved by the individual alone. When two people work together, the energy that is produced is greater than the sum of their individual effects. Such is the power of cooperation.
Source: Tafsir Naumne, Ayatullah Nasir Makarim Shirazi (ed.)