In the previous parts of this series, importance of Imamate in Shi‘i Islam was discussed. In doing so, narrations of the Prophet regarding the necessity of simultaneously holding on to the Qur’an and the Ahlul Bayt (a) were presented. Using mainly Sunni sources, both the meaning and authority of Ahlul Bayt were studied. In this part, we will study one of the characteristics of divinely appointed leaders including both prophets and Imams, that is, infallibility. With respect to the Prophets, both Shi‘a and Sunni scholars agree on the necessity of infallibility with respect to the delivery of the message, but there are differences of opinions with respect to their personal life and the period before the prophethood. The Shi‘a believe in the Prophets’ and Imams’ infallibility during and before their mission both in their public and private lives.