What is al-istislah as a legal proof, which imams held this view, and what is an example of it?

Istislah, also known as al-Masalih al-Mursalah, is a method of inference mentioned by scholars of Usul al-Fiqh (principles of Islamic jurisprudence). Al-Khawarizmi defines it as "preserving the intent of the Sharia by repelling harm from the creation." Al-Ghazali defines it as "the existence of a meaning that suggests a ruling is rationally appropriate, and there is no agreed-upon basis for it." Ibn Burhan defines it as "that which is not based on any universal or particular principle."

It refers to a description for which there is no textual evidence to confirm or invalidate it, yet it brings about a benefit or repels a harm. The author of Maraqi al-Sa'ud provided examples of Istislah, including: dotting and writing the Mus'haf, Abu Bakr appointing Umar, minting coins, renewing the call to prayer, imprisonment, and establishing administrative departments (dawawin).

Some believe that only Imam Malik advocated this principle, but many fatwas (religious edicts) from the imams of the four schools of thought and others have relied on Istislah. Al-Zarkashi mentioned in Al-Bahr al-Muhit that scholars in all madhahib (schools of thought) consider the general appropriateness sufficient for al-Masalih al-Mursalah.