The Muhaddithun have stated that the above narration is actually is the statement of Sayyiduna ‘Ali ibn Abi Talib (radiyallahu ‘anhu) and not a Hadith of Nabi (sallallahu ‘alayhi wa sallam).

It may be quoted as the statement of Sayyiduna ‘Ali (radiyallahu ‘anhu).

Many senior scholars of Hadith such as Allamah ‘Iraqi, Sakhawi, Suyuti (rahimahumullah) and even those after them such as Allamah Mullah Ali Qari, Ajluni, and Zabidi (rahimahumullah) have mentioned this to be the statement of Sayyiduna ‘Ali (radiyallahu ’anhu). However, with the following wording: الناسُ نيامٌ فإذا ماتوا انتبهوا (See: Al-Mughni ‘An Hamlil Asfar, Hadith: 3611, Al-Maqasidul Hasanah, Hadith: 1238, Ad Durarul Muntathirah, Hadith: 427, Al-Asrarul Marfu’ah, Hadith: 555, Kashful Khafa, Hadith: 2794, and Ithafus Sadah al Muttaqin, vol. 8 pg. 107)

 The same statement has also been reported from the following predecessors with their respective chains of narrators:

1. Sufiyan Thawri (rahimahullah) (Hilyatul Awliya, Hadith: 9576)

2. Sahl ibn ‘Abdillah Attustari (See Az-Zuhudul Kabir of Bayhaqi, Hadith: 523 and Kashful Khafa, Hadith: 2794)

And Allah Ta’ala Knows best

https://hadithanswers.com/hadith-people-are-asleep-when-they-die-they-will-wake-up/
https://hadithanswers.com/sayyiduna-alis-radiyallahu-anhu-statement-on-people-are-asleep/