Tafsir of Ta-Ha 20:120

(Then Satan whispered to him): This refers to the act of whispering (waswasa) to him. As Al-Raghib stated, it is the base thought or suggestion, and its root originates from al-waswas, which is the sound of jewelry or a faint whisper. Al-Layth said: Waswasa is the discourse of the self. The verb is waswasa, constructed for the active subject. It is said: a man is muwaswis (in the active case); using the kasra [for the active] and the fatha [for the passive] is a linguistic error.

Many have mentioned that waswasa is an intransitive verb derived from al-waswasa, which is an imitation of sounds, like the wailing of a bereaved woman, the howling of a wolf, or the clucking of a hen. When it is transitive with "to" (ila), it implies the meaning of "conveyance" (inha’). When it is followed by the particle "for" (lam), as in waswasa lahu, it is for clarification, as in the phrase hayta laka ("Come hither"). Al-Zamakhshari said: It is for the sake of [the person], meaning he whispered for his sake. It is the same when it appears after similar verbs, such as the saying: "Ring for her, O son of Abi Kubash, for she has no fodder tonight." In al-Asas, he mentioned waswasa ilayhi in the category of literal meaning; its apparent form suggests that the implication [of another verb] is not considered, whereas the majority hold that it is.

(He said): This is either a substitute for [the act of] "whispering," or an initiation of speech that serves as an answer to a question arising from the context, as if it were said: "What did he say to him during his whispering?" So it was answered: He said, (O Adam, shall I guide you to the tree of eternity): He called him by his name so that he would turn toward him and be more receptive to listening, then he presented to him what he presented in the form of an interrogation that implies sincerity. The meaning of "the tree of eternity" is a tree such that whoever eats from it remains forever and does not die at all, whether he remains in his state or becomes an angel, according to the words of the Exalted: "Unless you both become angels or become among the immortals."

In al-Bahr, it is stated that what is narrated here precedes what is narrated in [Surah] al-A’raf, starting from the words of the Exalted: "Your Lord did not forbid you from this tree..." and so on. When the accursed one saw a degree of inclination from him—upon him be peace—toward what was presented to him, he moved on to informing [him of its effects] and restricting [it to those benefits]. The truth is that there is no certainty regarding what was mentioned.

(And a kingdom that does not wither): That is, it does not vanish, nor does it become worn out or decrepit. It has been said that this is one of the necessities of eternity, so he mentioned it for emphasis and to increase the temptation.