The english of translation of Tafsir Ibn Kathir is abridged and omits some of the hadith quoted after this sentence:
There are Hadiths that mention that Allah took Adam's offspring from his loins and divided them into those on the right and those on the left.
As for this sentence:
At-Tirmidhi said, "This Hadith is Hasan Sahih, and it was reported from various chains of narration through Abu Hurayrah from the Prophet ''. Al-Hakim also recorded it in his Mustadrak, and said; "Sahih according to the criteria of Muslim, and they did not record it.''
It is regarding the hadith that has been quoted just before:
At-Tirmidhi recorded that Abu Hurayrah said that the Messenger of Allah said,
[ arabic text ]
(When Allah created Adam ...
... his offspring made mistakes.)
This is from Jami at-Tirmidhi, Kitab al-Tafsir, 3076 and has also been collected by al-Hakim Nishapuri in his Mustadrak ala al-Sahihain, Kitab al-Tafsir, Surah Al-A'raf, 3257. Mustadrak is a collection of hadith that the author claims them to be Saheeh on the conditions of Bukhari and Muslim.