Tafsir of An-Nazi'at 79:20

"Then he showed him the greatest sign." This is an eloquent expression that conveys several omitted sentences, relying upon their detailed explanation in another location. It is as if it were said: "So he went, and such and such occurred, and then he showed him..." Al-Zamakhshari limited himself in the marginalia to the estimation of a single sentence, stating that this is conjoined to an omitted element, with the intended meaning being: "So he went, and he showed him," because the Almighty’s statement, "Go," serves as an indication of this. It is similar to the verse, "Strike the rock with your staff, and there gushed forth..."

The act of "showing" (al-ira'ah) is either in the sense of causing him to see or in the sense of making him recognize, for when the accursed one saw them, he recognized them, and his claim of them being sorcery was merely a display of defiance. Attributing the showing to him—peace be upon him—is from the perspective of the apparent, just as attributing it to the Nun of Majesty in the Almighty's saying, "And We showed him Our signs," is from the perspective of reality.

The "greatest sign," according to what has been narrated from Ibn Abbas, is the transformation of the staff, for it was the forerunner and the primary event, while the other was like a corollary to it. According to what has been narrated from Mujahid, it is that and the White Hand, for in terms of indication, they are as a single sign. They were referred to in the plural form in the Almighty’s saying, "Go, you and your brother, with My signs," due to the wondrous matters contained within them, each of which is a clear sign for a people who reason. It is also permitted that it refers to the totality of his miracles—peace be upon him—with the singular form used in view of what was mentioned. The fa (then) indicates the immediate succession of the first of them, or the totality of them based on the first. It is termed "the greatest" relative to the miracles of the messengers before him—peace be upon them—or it may be for absolute emphasis, though its distance [from the intended meaning] is not hidden. Increasing its distance is the ordering of the gathering of the sorcerers thereafter, for that did not occur except upon the showing of those two signs and his turning away from acting in accordance with them. As for the nine [signs] other than those two, they only appeared at his hands—peace be upon him—after he had defeated the sorcerers, over time, spanning about twenty years.

The extremists among the Shia claimed that the "greatest sign" is Ali—may Allah ennoble his countenance—whom He showed to him with his noble soul manifesting in its greatest form. This is raving that lies beyond reason and the bounds of textual transmission.