As stated by @UmH in the given answer the translation used on sunnah.com here was inconsistent and didn't mention the real narrator of the narration from Sahih Muslim.
Because the narration is a report of a conversation between abu Sirmah and abu Sa'id al-Khudri.
Abu Sirmah أبو صرمة is referred to according to Muhammad al-Amin al-Harari محمد الأمين الهرري (died 2019) in his commentary on Sahih Muslim called "al-Kawkab al-Wahhaj wa ar-Rawd al-Bahhaj fi sharhi Sahih Muslim ibn al-Hajjaj الكوكب الوهاج والروض البهاج في شرح صحيح مسلم بن الحجاج" (See here and in the following page) -with some edition- as:
(أنه قال: دخلت أنا وأبو صرمة) ... مالك بن قيس، وقيل: قيس بن مالك بن أبي أنس الأنصاري المازني المدني الصحابي المشهور شهد بدرًا وما بعدها، روى عن النبي صلى الله عليه وسلم وعن أبي أيوب الأنصاري في التوبة، ويروي عنه (م عم) وعبد الله بن محيريز ومحمد بن كعب القرظي وغيرهم، قال الحافظ في النكاح: صحابي مشهور، ثم قال في القدر: مختلف في صحبته
(That he and abu Sirmah entered...) ... Malik ibn Qays, it was also mentioned Qays ibn Malik ibn abi Anas al-Ansaari al-Maazini al-Madani the known sahabi (companion) who witnessed Badr and what came after. He narrated on the authority of the Prophet, may Allah's prayers and peace be upon him, and on the authority of Abu Ayyub al-Ansari in (topic of) repentance, and narrated on his authority (م(according to al-Maaziri in his al-Mu'alim) عم (unclear to whom he is referring here basically with "ع" the author refers to Qadi 'Iyad in his Ikmal and "م" was already mentioned, but I couldn't find so far a definition for "عم")) , Abdullah ibn Muhairiz, Muhammad ibn Ka’ab al-Quradhi and others. Al-Hafiz (ibn Hajar) said in an-Nikah: A well-known companion, then he said in al-Qadr: There is a difference in his companionship
Abu Sirmah is mainly regarded as a Sahabi however ibn Hajar seems to have mentioned two different opinions on his companionship in his book(s).
A known hadith which was reported by him is:
The Prophet (ﷺ) said: If anyone harms (others), Allah will harm him, and if anyone shows hostility to others, Allah will show hostility to him.
This was among others compiled by abu Dawod in his Sunan and a-Tirmidhi in his Jami'