Tafsir of Al-Muddathir 74:17

Al-Muddaththir: (17) I will surely subject him to arduous ascent (Sa'urhiquhu ṣuʿūdan).

Translation:

I will surely subject him to an arduous ascent.

Regarding the meaning of ṣuʿūd (ascent), there are two views:

1. It is a metaphor for the severe, difficult, and unbearable torment he will face, similar to His saying: {He will cause him to enter a steep ascent} (Al-Jinn: 17). Ṣuʿūd is derived from the phrase ʿaqabah ṣuʿūd (a difficult, steep pass), which is arduous and hard to ascend.
2. It is the name of a mountain in the Fire. Whenever he places his hand upon it, it melts; when he lifts it, it reforms. When he places his foot upon it, it melts; when he lifts it, it reforms. It is narrated from the Prophet (peace be upon him): "Al-Ṣuʿūd is a mountain of fire; he will ascend it for seventy autumns, then fall down similarly, forever."

Then, the Almighty recounts the manner of his obstinacy:

{Indeed, he thought and plotted.} (74:18)