Fasid (Arabic: فاسد) is an Islamic religious concept refers to corruption. It refers to corruption created by humans. This corruption can only be caused by humans, as they are made of clay, which can manifest darkness and evil.

The antonym of fasid is salih (wholesomeness) or salihat (righteous deeds).

One manifestation of fasid is the human desire to control nature. Since nature, as with all things, is under the government of Allah, such an attempt becomes an act of insubordination and a rejection of Allah's Will.