Tafsir of Az-Zukhruf 43:86

"And those whom they invoke do not possess..." That is, their gods whom they invoke— "...other than Him..." —any power of intercession, as they falsely claimed that these beings were their intercessors before Allah, the Almighty and Majestic. It is also recited as tadʿūn (you invoke) with the tāʾ of address and the lightened dāl. Al-Sulami and Ibn Waththab recited it with the dāl intensified [shaddah].

"...except those who bear witness to the truth..." Which is the Oneness of God (tawhīd).

"...while they know." Meaning, they possess knowledge of it. The clause is in the position of a state (hāl). It is qualified with this because testimony given without knowledge of what is being testified to cannot be relied upon. The pronoun is used in the plural form based on the meaning of man (who/those), just as it was used in the singular form [in the preceding verb] based on its wording. By this, it is meant the angels, ‘Īsā, ‘Uzayr, and their like—may the blessings and peace of Allah the Exalted be upon them.

Regarding the exception (istithnāʾ): it is said to be connected (muttasil) if what is intended by "those whom they invoke other than Him" is everything worshipped besides Allah, the Almighty and Majestic. It is disconnected (munfasil) if what is intended by that is idols alone. It is also said that it is disconnected in all cases, and it is argued that the intention is to negate the ability of false gods to intercede for the disbelievers. Even those among them who bore witness to the truth do not possess the ability to intercede for them [the disbelievers]; they only possess the ability to intercede for the believers. Therefore, it is as if it were said, upon the assumption of generality: "Those whom they invoke other than Allah, the Exalted—whoever they may be—do not possess the power of intercession for them [the disbelievers]. However, those who bore witness to the truth do possess the ability to intercede for whom Allah, the Glorified, wills among the believers." Thus, the statement is similar to your saying: "None of the people came to me except Zayd came to ‘Amr." So, reflect upon this.

Mujahid and others said: The intention behind "those who bear witness to the truth" is the ones for whom intercession is made (al-mashfūʿ fīhim). In this view, the exception is connected, and the object of the exception (mustathnā minhu) is elided. It is as if it were said: "These angels and their like do not possess the power of intercession for anyone, except for those who affirmed the Oneness of God with certainty and sincerity." Similar to this in the elision of the object of the exception is the verse: "Sālim escaped, and his soul was choking; and nothing was saved except the scabbard of a sword and a waist-wrapper," meaning: "Nothing was saved except the scabbard of a sword and a waist-wrapper."

The verse is used as evidence that knowledge is indispensable in testimony, unlike mere witnessing (mushāhadah).