Qadariyah (or Qadariya), in Islam, are adherents of the doctrine of free will. The word Qadar is derived from qadr (power or rights).
Qadariya was one of the earliest philosophical schools of thought in Islam. The doctrine espoused notions of rationalism and contained elements of Greek philosophy. Qadaris maintain that Allah gave man free will, without which one cannot be fully accountable for one's actions. Free will also means that Allah cannot know a man's actions in advance. Qadaris also deny other core tenants of Sunni belief including the belief in the Punishment of the Grave. They also deny that an authentic hadeeth is an evidence for establishing a proposition in the Islamic aqeedah unless it is transmitted in mutawatir form.
According to Sunni sources, the Qadariyah were censured by Muhammad himself by being compared to Zoroastrians, who likewise deny predestination. It is reported in Sunan Abu Dawood: Narrated Abdullah ibn Umar: The Prophet said: "The Qadariyyah are the Magians of this community. If they are ill, do not pay a sick visit to them, and if they die, do not attend their funerals."