Who is shaitan referring to in verse 38:79

Question

In verse 79 in Surah Sad, after Shaitan refused to bow down before Adam (AS):

He said, "My Lord, then reprieve me until the Day they are resurrected."

Is shaitan referring to the resurrection of humanity on Day of Judgement? If so, did he already know Allah's plan to send Adam (AS) to earth, spread humanity, etc.?

If not, was he referring to life that had already passed away? If so, what life was he referring to?

Answer 1

Yes, Shaytan is referring to the resurrection of humanity here on the Day of Judgement. he was not referring to life that had already passed away.

[7:14] Said he, ‘Reprieve me, postpone my affair, until the day when they, people, are resurrected’.

^{Tafsir Al-Jalalayn}

[38:79] He said, ‘My Lord, then reprieve me until the day when they, mankind, will be raised’.

^{Tafsir Al-Jalalayn}

But before Shaytan asked Allah for a reprieve, Allah informed him that Shaytan would be condemned until judgement day, so that is how he knew about the day of resurrection or judgement.

And surely upon you is condemnation until the Day of Judgment.”

^{Quran 15:35}

Satan appealed, “My Lord! Then delay my end until the Day of their resurrection.”

^{Quran 15:36}

You can read more about this topic here.

Answer 2

Qurtubi writes:

وقال : إلى يوم يبعثون ولم يتقدم ذكر من يبعث ; لأن القصة في آدم وذريته ، فدلت القرينة على أنهم هم المبعوثون

He said: 'until the Day they are resurrected' and did not first mention who will be resurrected. Since this story is about Adam and his children so context evidences that they are the ones who will be resurrected.

^{— Tafsir al-Qurtubi}

AFAIK nowhere is it explicitly stated that Adam (عليه السلام) was supposed to live in paradise forever at that time - rather you are wrongly assuming that. When creating Adam , Allah says to the angels that His plan is to place humanity on 'earth', which is evidence that Adam was going to leave paradise eventually:

وإذ قال ربك للملائكة إني جاعل في الأرض خليفة قالوا أتجعل فيها من يفسد فيها ويسفك الدماء ونحن نسبح بحمدك ونقدس لك قال إني أعلم ما لا تعلمون

And [mention, O Muhammad], when your Lord said to the angels, "Indeed, I will make upon the earth a successive authority." They said, "Will You place upon it one who causes corruption therein and sheds blood, while we declare Your praise and sanctify You?" Allah said, "Indeed, I know that which you do not know."

^{— Quran 2:30}

Further the temptation that Satan uses against Adam is one of Eternity:

فوسوس إليه الشيطان قال يا آدم هل أدلك على شجرة الخلد وملك لا يبلى

Then Satan whispered to him; he said, "O Adam, shall I direct you to the tree of eternity and possession that will not deteriorate?"

^{— Quran 20:120}

وقال ما نهاكما ربكما عن هذه الشجرة إلا أن تكونا ملكين أو تكونا من الخالدين

(Satan) said, "Your Lord did not forbid you this tree except that you become angels or become of the immortal."

^{— Quran 7:20}

Which indicates that both Adam and Satan knew that Adam was not going to live there forever by default.

Eternity in paradise only applies to the humans who would enter it as a reward.