refuted by al-Kindi , [104] followed by Abū Rayhān al-Bīrūnī , [105] Avicenna , [106] and Ibn Khaldun . In his Doubts about Galen , al-Razi was the first to prove both Aristotle 's theory of classical elements and Galen 's theory of humorism false using an experimental method. [107] Nasīr