One famous quote by al-Kindi is "Knowledge is the food of the soul." This quote reflects his belief in the importance of seeking knowledge and understanding in both philosophical and scientific pursuits. Another notable quote is "The first step in the acquisition of wisdom is silence, the second listening, the third memory, the fourth practice, the fifth teaching others." This quote highlights al-Kindi's emphasis on the process of gaining wisdom through learning, reflection, and sharing knowledge with others.