The hadith notes that the faith of devout Muslims in the End Times will be most acceptable, insha'Allah. The Muslims described in the hadith are Hazrat Mahdi (as) and his students. Their imam will be imprisoned from time to time and will sometimes be far removed from them. The reference in the hadith to "black on white" is the black writings on white paper, in other words, to books. There will be a huge growth in belief thanks to books describing the signs leading to faith. This is how the way that Muslims in the End Times will possess faith by means of books is described.