Wikipedia
Maslaha or maslahah (, "public interest") is a concept in traditional Islamic law. Maslaha is not Shari'a, but it is a concept that belongs to Islamic jurisprudence (also known as fiqh). It is one of the secondary sources in Islamic jurisprudence used by some "madhhab" to interpret Shari'a (the general principles present in the Qur'an and the Sunnah) in order to set rules. It is invoked to prohibit or allow something on the basis of whether or not it serves the common good or public welfare.
The concept is related to that of istislah. While the meaning of maslaha is "public interest", the meaning of istislah is "to seek the best public interest"—the Sharia's object and purpose.
Maslaha was used in one sense by the Andalusian lawyer al-Shatibi (d. 1388), who focused on the motivations behind the Islamic law. Regarding questions related to God, 'ibadat, humans should look to the Qur'an or the Sunnah for answers, but regarding the relationship between humans, mu'amalat, humans should look for the best public solution. Since societies change, al-Shatibi thought that the mu'amalat part of the Islamic law also needed to change.
Maslaha has also been used by several Muslim reformers in recent centuries. Al-Wahhab (d. 1792) used maslaha in a few cases. The concept is more known to Islamic modernists. Among them, Muhammad Abduh is especially recognized for using the concept of maslaha as the basis for reconciling modern cultural values with the traditional moral code of Islamic law in the late 19th century. The Muslim Brotherhood, an Islamic fundamentalist group, also invokes maslaha to explain their commitment to public welfare.