The Mahdi belief had reappeared during the 'Abbasid Revolution as a provocative force for the masses not long after its spread in Islamic society. For this reason, in many studies on the revolution, how and in what way this belief was utilized have been discussed. The 'Abbasids exploited expectation of saviour, which was identified as the Mahdi belief, to legitimize themselves in the caliphate even after the revolution succeeded. Thus, in the Akhbar al-Abbas, which is considered the semi-official history of the 'Abbasid Revolution, there are many riwayas emphasizing that the 'Abbasids are the expected saviours. Akhbar al-Abbar is an anonymous manuscript which provides essential information about the revolution and therefore probably had been written by someone close to the 'Abbasid family. After the publication by 'Abd al-Aziz Dari and A. J. al-Muttalibi in 1971, the manuscript became known as Akhbar al-Abbas, and Akhbar in short. There are many riwayas in this source which emphasize that the 'Abbasids are the expected saviours. These riwayas are mostly presented with narratives about the appearance of black banners. Although the riwayas in the manuscript have been discussed to shed light on various aspects of the revolution in the studies which investigate or reference this source, there is no study emphasizing that there is a direct relationship between these riwayas and Mandi belief. Moreover, the riwayas in the source have not been examined in detail. There are two topics which need to be focused on when reviewing the literature. Of these two, the more important is the Akhbar. Studies on this newly discovered source have been about the 'Abbasid Revolution and, recently, on the historiographical value and authenticity of the source. The other focus of these studies is the Mandi belief and its importance for the revolution, which has been studied for more than a century. Gerlof Van Vloten's book can be regarded as the primary work to reveal some important challenges for the Mahdi belief and its effect on the 'Abbasid Revolution. However, Van Vloten did not refer to Akhbar because the manuscript had not been discovered yet when he published his study at the end of the 19th century. This article was written to discuss the influence of the Mandi (saviour or deliverer) belief in the 'Abbasid Revolution through riwayas on black banners. It points out the riwayas of the black banners in the Akhbar by associating them with the Mandi belief. For this reason, the title "Mahdi with Black Banners" was chosen for this article. Modern historians believe that this belief had become widespread in the Islamic society gradually and thus was influential in the 'Abbasid movement; however, the available sources were not enough to support this claim sufficiently. In this study, firstly the Mandi belief will be explained. Then the importance of Mahdi belief during the 'Abbasid movement will be discussed. And finally, the riwayas related to this belief in the Akhbar will be examined in more detail compared to the similar studies. In conclusion, the article argues that despite the minority of the direct riwayas on the Mandi belief, there are many riwayas in Akhbar about the black banners. Thus, it can be said that the 'Abbasids took advantage of Mandi belief for the success of the revolution and to gain legitimacy afterwards. However, this belief was not only Mandi but Mandi with a black banner.