Technical note / Defect ('illah): In the manuscripts "wa nahwahu" is written, whereas what we have recorded in the text is the correct wording according to al-Dhahabi's "al-Talkhis" and the other takhrij sources.

Grading: With this wording this narration is "gharib", and its chain is da'if.
Technical note / Defect ('illah): Sharik bin Abd Allah (al-Qadi) is alone in narrating it with this chain as marfu', whereas a group transmitted it through another chain as "mawquf" (a saying of a Companion), as will come later. The narrator Abu Sadiq (al-Azdi al-Kufi) was declared thiqah by Ya'qub bin Shaybah, Abu Hatim called him "mustaqim al-hadith" (sound in hadith), while Ibn Sa'd says that his hadiths are few and he has been criticised.

Note / Clarification: Uthman bin Abi Zur'ah is Ibn al-Mughirah al-Thaqafi, and Abd al-Rahman bin Yazid is Ibn Qays al-Nakha'i (the brother of al-Aswad).
Reference / Source: Ibn Abi al-Dunya narrated it in "Sifat al-Jannah" (216) via Uthman bin Abi Shaybah, with this same chain, in these abridged words: "Paradise has eight gates".

Reference / Source: This narration was transmitted in full and in abridged form by Abd Allah bin Abi Shaybah (Musnad 307), al-Darimi (2860), Abu Ya'la (5012), al-Tabarani (al-Kabir 10479) and Abu Nu'aym (Sifat al-Jannah 169) via various routes from Mu'awiyah bin Hisham.

Reference / Source: Abu Nu'aym (169) narrated it via Ali bin Shubrumah, from Sharik bin Abd Allah.

Important point: This is a mawquf saying of Ibn Mas'ud (may Allah be pleased with him).
Details of the narration: A man who had committed a sin came to Ibn Mas'ud (may Allah be pleased with him); he at first turned away from him, then when he saw tears in his eyes he said: "Now is the time for your concern over what you came for. Paradise has seven gates which open and close until the Day of Resurrection, except the gate of repentance, over which an angel is appointed; so do good deeds and do not despair".
Reference / Source: Ibn Fudayl (al-Du'a 139), Sufyan bin Uyaynah (Zawa'id al-Zuhd 1042) and Abu Awanah (Usul al-I'tiqad 2010) narrated it through Abu Sinan (Dirar bin Murrah), from Ya'qub bin Ghadban.
Technical note / Defect ('illah): No one narrated from Ya'qub bin Ghadban except Abu Sinan; Ibn Hibban did mention him in "al-Thiqat", but at the same time said: "I do not know who he is".

Corroborating chains and supporting reports: On the topic of Paradise having eight gates, it is supported by the hadith of Sahl bin Sa'd (may Allah be pleased with him) in Sahih al-Bukhari (3257) and the hadith of Ubadah (may Allah be pleased with him) in Sahih Muslim (28).

General principle: That the gate of repentance is open is established by numerous proofs from the Qur'an and Sunnah, some of which the author (al-Hakim) has mentioned in earlier chapters.