Grading: Its chain is sahih.
Technical note / Defect ('illah): There is a disagreement over Isma'il bin 'Ulayyah concerning the identity of his shaykh; with the author (al-Hakim) the shaykh's name is "Yunus" (Yunus bin 'Ubayd), whereas with others it is "Ayyub al-Sakhtiyani". Since Ibn 'Ulayyah is a student of both, it is possible that he heard it from both. In any case, whichever way the chain goes, it ends with a trustworthy (thiqah) narrator.
Important point: Imam al-Hasan al-Basri's hearing (of hadith) from Abu Barzah (may Allah be pleased with him) is sound, as Abu Hatim said. Although Ibn al-Madini denied it, the statement of Abu Hatim is correct, because al-Hasan al-Basri was contemporary with Abu Barzah in Basra for a long time and Abu Barzah died late, so there is no reason to deny the hearing.

Reference / Source: Imam al-Bayhaqi narrated it at (9/ 60) via Abu 'Abd Allah al-Hakim (the author) with this same chain.

Reference / Source: Ahmad bin Mani' narrated it in his Musnad, as mentioned in al-Hafiz Ibn Hajar's "al-Matalib al-'Aliyah" (3162).

Details of the narration: Al-Tabarani narrated it in "al-Mu'jam al-Kabir" (226) by way of Muhammad bin Sallam al-Jumahi, and Ibn 'Asakir in "Tarikh Dimashq" (62/ 96) by way of Abu 'Ammar Husayn bin Hurayth. All of them, narrating from Isma'il bin 'Ulayyah, gave the shaykh's name as "Ayyub al-Sakhtiyani", not Yunus bin 'Ubayd.

Reference / Source: Ibn Abi Shaybah (8/ 277, 12/ 249), Ibrahim al-Harbi in "Gharib al-Hadith" (1/ 329) and al-Tabarani narrated it by way of Hushaym bin Bashir from Yunus bin 'Ubayd.

Reference / Source: Ibn Qani' narrated it in "Mu'jam al-Sahabah" (3/ 159), and Ibn 'Asakir by way of al-Harith bin 'Umayr from Ayyub al-Sakhtiyani.

Note / Clarification: The word of the hadith "ajhadnahum" means: "we drove them away from that place and forced them to hurry".

Note / Clarification: The "'itfa" (two sides) of a person are both his flanks from the head down to the hip; they are given this name because a person leans (inclines) on them.