Technical note / Defect ('illah): In manuscript (B) this word has been corrupted into "'Amr".

Grading: Its chain is hasan on account of 'Ubaydullah bin 'Abdullah bin al-Asamm.
Reference / Source: Al-Hafiz Ibn Hajar also declared it hasan in "Fath al-Bari" (20/ 297).
Technical note / Defect ('illah): However, there is disagreement over whether this hadith is marfu' (a saying of the Prophet, peace and blessings be upon him) or mawquf (the statement of a Companion).

Corroborating chains and supporting reports: Ibn Mallas is corroborated in narrating this hadith as marfu' by Abu 'Abd al-Rahman 'Abdullah bin 'Umar Mushkadanah, as narrated by Ibn Abi al-Dunya in "al-Ahwal" (46) and (52), by Abu Nu'aym in "al-Hilyah" (4/ 99), and by Ibn Qudamah in "Ithbat Sifat al-'Uluww" (39), and via him by al-Dhahabi in "al-'Uluww" (90). Likewise he is corroborated by Yahya bin Ma'in, as in Abu Mansur al-Shaybani's "Juz' min Hadithihi" (14), and by Abu Kurayb Muhammad bin al-'Ala', as in Abu al-Shaykh's "al-'Azamah" (391). These three (Mushkadanah, Ibn Ma'in and Abu Kurayb) narrate it from Marwan al-Fazari with this chain as "marfu'" (as a saying of the Prophet, peace and blessings be upon him).

Technical note / Defect ('illah): They (those narrating it as marfu') were contradicted by 'Abd al-Jabbar bin al-'Ala' (with Abu al-Shaykh: 392) and Dawud bin Rushayd (in al-Lalaka'i's Usul al-I'tiqad: 2185). Both of them narrated it from Marwan al-Fazari with this chain as "mawquf" on Ibn 'Abbas (may Allah be pleased with him), as his own statement. (Note that) all five of these narrators are thiqah.

Corroborating chains and supporting reports: 'Abd al-Wahid bin Ziyad also narrated it from 'Ubaydullah bin 'Abdullah bin al-Asamm with this chain as "mawquf".
Reference / Source: It was recorded by Ibn Abi al-Dunya in "al-Ahwal" (51). And 'Abd al-Wahid is a "thiqah" narrator.

General principle: Such a report (concerning the unseen) cannot be stated merely from one's own opinion or reasoning, so it has the ruling of "marfu'" (i.e. it is to be regarded as a saying of the Prophet, peace and blessings be upon him).

Corroborating chains and supporting reports: Among the marfu' narrations, the hadith of Anas bin Malik (may Allah be pleased with him) with similar wording serves as a shahid (supporting report) for it; it is in al-Khatib al-Baghdadi's "Tarikh Baghdad" (6/ 365-366) and al-Diya' al-Maqdisi's "al-Mukhtarah" (7/ 2567).
Technical note / Defect ('illah): All its narrators are thiqah except one narrator, "Ahmad bin Mansur bin Habib", whose status is unknown (majhul al-hal). For more, see what follows it.

Note / Clarification: The words of the hadith "in tarafa" mean "ma tarafa" (i.e. he did not even blink), as stated explicitly in the source works of the takhrij. The word "in" here is negative, in the sense of "ma" (not).

Note / Clarification: "Al-sur" is the horn (trumpet) into which (for the Hour) a blast will be blown.