"Muhammad and 'Ali both were manifestations of one and the same Divine Light*, but they came in two different persons (libas,–dress) in order to uphold each other's mission amongst humans, and in order to introduce each other to the people. However, the people did not recognize them. Salman Farsi said in Persian, on the day when Abu Bakr was in appearance (zahir) elected as a caliph: 'kardid–na-kardid,' i.e., 'you have done this, and yet you have not done it.' He meant that they had appointed a lieutenant to the Prophet, and yet, in reality, nothing had been done. But this is a long story, O, God!
 
The holy Light which manifested in Muhammad and 'Ali continued in the world through Fatima, in her sons, Hasan and Husayn, and no power in the world can extinguish this Light. It is said (Holy Qur'an 9:32): 'they wanted to extinguish the Light of God, but God brings His light through, to the end,' i.e., to the completion of its mission.
 
Even if traitors and apostates dislike this, how can this Light disappear from the world? Or how should it return to its Source without accomplishing what it was destined to accomplish?
 
Therefore those people who are born later, what have they to do, and whom have they to follow, so as not to stray from the right path? And even if they do not recognize it, and wantonly go on a wrong path, God, nevertheless, has to manifest a Guide (hujjat), who should be with them."
 

(Pir Shihabu'd-din Shah Al-Hussaini, p.25)