This is particularly evident in the asceticism, austerity, and renunciation of worldly possessions that he practiced in his life. Historians, despite their differing perspectives on him, agreed on this point. Ibn Khaldun mentioned that he "used to wear a patched cloak. He had a long history of asceticism and worship."

Ibn Khallikan mentioned that "his sustenance was a loaf of bread each day from the spinning of his sister, with a little ghee or oil. He did not deviate from this even when the world's riches came his way." One day, his companions were tempted by the abundance of spoils they had gained. He ordered all of it to be gathered and burned, saying: "Whoever follows me for worldly gain, has no claim on me. Whoever follows me for the Hereafter, his reward is with Allah Almighty."

Ibn al-Athir said of him that he "was pious and devout." Ibn Taymiyyah said of him that "he had an element of asceticism and worship."

These testimonies, despite their different sources, prove that the Mahdi was sincere in his faith in his Lord and truly submissive to Him. Asceticism in this world and renunciation of its pleasures, when the means for luxury and indulgence are available, is an objective proof of sincerity in faith and truthfulness in it. This sincerity reaches its highest degree when the intellectual conviction of the entire Islamic creed becomes a subject for preaching to others and striving to generalize it and make it a way of life for people. This is what Ibn Tumart pursued in his constant enjoining of good and forbidding of evil. As we mentioned earlier, on his way back from the East, he exposed himself to hardships and dangers in order to call people to implement Sharia and adhere to its teachings. There was no village or city he passed through from the time he left Mecca until he reached his village, except that he was there "severely denouncing people for what contravened Sharia, not content with anything less than the manifestation of God's command. He was naturally inclined to find satisfaction in this, enduring harm from people because of it." Ibn Khaldun, Al-'Ibar: (13) Ibn Khallikan, Wafayat al-A'yan: (14) Ibn al-Athir, Al-Kamil: (15) Ibn Taymiyyah, Majmu' al-Fatawa: (16) Sincerity to an idea does not reach its highest degree except when it becomes a driving force for preaching it and calling to it. (17) Ibn Khallikan, Wafayat al-A'yan: (18) 135