Muhammad bn Abdulkareem Ash-Shahrastaani (d.549AH), the author of the popular al-Milal wan-Nihal, was very vast in knowledge but his venturing into scholastic theology made his knowledge a waste.
Ibn Ar'salaan said about him: 'He was knowledgeable...if not his venturing into theology, and his missteps in Aqeedah, he would have been a Imaam. We do wonder about him that despite what he had been honoured with, he still went after some baseless knowledge. We seek protection in Allaah from disgrace. Nothing but his shunning the knowledge of the Sharee'ah and his getting busy with the darkness of philosophy. We have had talks with him, we used wondered how he was so adamant on his helping and defending philosophy. I was present in many of his admonitions, there was nothing like 'Allaah said His Messenger said in them...'
As-Siyar 15/89
