Wala yamliku allatheena yadAAoona min doonihi ashshafaAAata illa man shahida bilhaqqi wahum (surah Zukhruf: 86)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(43:86) Those whom they call upon, instead of Allah have no power of intercession, except such that testify to the truth based on knowledge. *68

Wa laa yamlikul lazeena yad`oona min doonihish shafaa`ata illaa man shahida bilhaqqi wa hum ya`lamoon

*68) This sentence has several meanings:
(1) Those whom the people have made their deities in the world, will not at all be their intercessors before Allah. Those of them who were wicked, will themselves be presented as culprits there. However, those who had borne witness to the Truth by virtue of knowledge (and not unconsciously) will certainly be able to intercede for others.
(2) Those who will be permitted to intercede, will be able to do so only for those who had testified to the Truth consciously (and not heedlessly). They will neither intercede of their own will, nor will have the permission to intercede for anyone who had gone and been led astray from the Truth in the world, or had been affirming the faith in Allah as the only Deity unconsciously as well as serving other deities at the same tithe
(3) If a person says that those whom he has made gods necessarily possess the powers of intercession, and they wield such an influence with Allah that they can have anyone they like forgiven, irrespective of his beliefs and deeds, is totally wrong. No one enjoys such a position with Allah. If the one who claims that another has such powers of intercession, can testify to the truth of this matter by virtue of knowledge, one should have the courage to say so. But if one is not in a position to bear such a testimony, and one is certainly not, it would be sheer folly to invent such a creed on the basis of mere hearsay, or conjecture, and risk one's life hereafter relying only on an imaginary support.
Incidentally, this verse also gives two important principles: First, it shows that bearing a testimony to the truth without knowledge may be reliable in the world, but it is not so before Allah. In the world, whoever affirms the Faith verbally will be regarded as a Muslim and treated as such unless he openly commits an act expressly contradictory to belief. But as before Allah only such a one will be counted as a Muslim, who has uttered L8 ilaha ill-Allah consciously, with full understanding of what he is denying and what he is affirming according to his best knowledge.
Secondly, it gives this principle of the law of cvidence that knowledge is a pre-requisite of bearing the cvidence. If the bearer of an evidencc has no knowledge of the event to which he is bearing evidence, his evidencc is meaningless. The same is borne out by a decision given by the Holy Prophet. He said to a witness: "If you saw what happened with your own eyes as you are seeing the sun, then you may bear the witness, otherwise not." (Ahkam al-Qur an by al Jassas).