Imam Sadiq (peace be upon him): While my father was performing tawaf around the Kaaba, suddenly a man who had covered his face with the corner of his turban made way for him so that he could complete his seven circuits of tawaf. Then he took him to a house next to Mount Safa and sent for me, and [in that house] there were only the three of us. [Some words were exchanged between us, and in the course of the conversation he turned to my father and] said: ... 'Inform me about the knowledge that whoever knows it will find no disagreement in it.' My father said: 'The entirety of knowledge is with Allah the Majestic, and that which the servants cannot do without is with the awsiya (successors).' ... That man said: 'I am Ilyas (peace be upon him). I do not ask you about the matter of [wilayah] out of my own ignorance, but rather I ask so that this discourse may be a source of strengthening for your companions, and I will inform you of a sign that you already know, [to use] if people dispute over it and persist.' My father said to him: 'If you wish, I will inform you.' He said: 'I do wish it.' He said: 'If our Shia say to our opponents that Allah says to His Messenger: إِنَّا أَنْزَلْنَاهُ فِی لَیْلَةِ الْقَدْرِ [Indeed, We sent it down on the Night of Decree] ... did the Messenger of Allah (peace be upon him and his family) come to know something of knowledge on that night which he did not know before, or had Jibra'il (peace be upon him) also brought him that knowledge on other than that night?' They will say: 'No.' Say to them (the opponents of the Shia): 'Then regarding what he knew, had he any option but to make it manifest?' They will say: 'No.' Then say to them: 'Is there any disagreement in what the Messenger of Allah (peace be upon him and his family) made manifest of the divine knowledge?' If they say: 'No,' say to them: 'Then given this, has anyone who rules that there is disagreement in the ruling of Allah opposed the Messenger of Allah (peace be upon him and his family)?' They will say: 'Yes.' And if they say: 'No,' they have contradicted their earlier statement. Then say to them: 'None knows its interpretation except those firmly rooted in knowledge (al-rasikhun fi al-'ilm).' If they ask: 'Who are the rasikhun (those firmly rooted)?' say: 'The one in whose knowledge there is no disagreement.' If they say: 'Who is he?' say: 'The Messenger of Allah (peace be upon him and his family) was the possessor of that. Did he convey it or not?' If they say: 'He conveyed it,' say: 'Did he depart from this world while his successor had knowledge of that in which there is no disagreement?' If they say: 'No,' say: 'The successor of the Messenger of Allah (peace be upon him and his family) is divinely supported, and the Messenger of Allah (peace be upon him and his family) chooses as his successor only one who rules by his ruling and who is like him in all things except prophethood. And if the Messenger of Allah (peace be upon him and his family) did not appoint anyone as his successor in his knowledge, then he would have wronged the generations that come after him.' If they say to you: 'The knowledge of the Messenger of Allah (peace be upon him and his family) was from the Quran,' say: 'حم* وَ الْکِتابِ الْمُبِینِ* إِنَّا أَنْزَلْناهُ فِی لَیْلَةٍ مُبارَکَةٍ إِنَّا کُنَّا مُنْذِرِینَ* فِیها یُفْرَقُ کُلُّ أَمْرٍ حَکِیمٍ* أَمْرًا مِّنْ عِندِنَا إِنَّا کُنَّا مُرْسِلِینَ [Ha Mim. By the clear Book. Indeed We sent it down on a blessed night; indeed We are ever warning. Therein every wise affair is decided, as a command from Us; indeed We are ever sending].' Then if they say: 'Allah the Mighty and Majestic sends [His command] only to a prophet,' say: 'This is the command of Allah the Wise, that He apportions among the angels and the Spirit that descends from a heaven to a heaven or from a heaven to earth [and assigns each of them to a task].' If they say: 'It was from a heaven to a heaven, since there is no one in the heavens who turns from obedience to disobedience,' or if they say: 'It was from a heaven to earth, since the people of the earth are the most in need of it among creation,' then say: 'Then is there any way left for them except that they refer to a master and elder who can judge in their disputes?' If they say: 'The caliph is the very one who judges for them,' then recite to them the word of Allah: اللهُ وَلِیُّ الَّذِینَ آمَنُوا یُخْرِجُهُمْ مِنَ الظُّلُماتِ إِلَی النُّور وَ الَّذینَ کَفَرُوا أَوْلِیاؤُهُمُ الطَّاغُوتُ یُخْرِجُونَهُمْ مِنَ النُّورِ إِلَی الظُّلُماتِ أُولئِکَ أَصْحابُ النَّارِ هُمْ فیها خالِدُونَ [Allah is the guardian of those who believe; He brings them out of the darkness into the light; and those who disbelieve, their guardians are the Taghut who bring them out of the light into the darkness; they are the companions of the Fire, they abide therein forever]. By my life! There is no wali (representative) of Allah the Mighty and Majestic in the earth or the heaven except that he is divinely supported, and whoever is divinely supported does not commit error or sin; and there is no enemy of Allah the Mighty and Majestic upon the earth except that he is forsaken, and whoever is forsaken never acts correctly. Just as Allah has commanded that there is no alternative but that this [master and sayyid] be sent from the heaven, so that the people of the earth may bring their disputes to him, there is no way and no alternative but the existence of a wali.'