“I have never struggled with anything harder than my own intention, for it keeps turning over on me.”

Sufyan al-Thawri (97–161 AH) was one of the great early jurists and hadith scholars of Kufa, a man whose knowledge was not in doubt — which is what gives the admission its weight. The saying is transmitted in the literature on sincerity and is quoted by Ibn Rajab among others: the difficulty he names is not learning or worship but keeping the intention still while doing them.