The Messenger of Allah ﷺ said, "Whoever is asked about knowledge and conceals it will be bridled with a bridle of fire on the Day of Resurrection."
حدثنا أبو كامل حدثنا حماد عن علي بن الحكم عن عطاء بن أبي رباح
قال رسول الله ﷺ من سئل عن علم فكتمه ألجم بلجام من نار يوم القيامة
The isnad is sahih. Hammad is Ibn Salama, Imam Basri. Ali bin Hakam is Banani Basri, whose reliability has already been established at 3141 and 5684.The hadith was narrated by Abu Dawud (3658) [3:360 of Awn al-Mabud], from Musa bin Ismail, and by Ibn Hibban in his Sahih (95, in our edition), through Nadr bin Shumayl, both of them from Hammad bin Salama, with this isnad. Likewise, Ibn Abdul-Barr narrated it in Jami Bayan Ilm (4:1), through Abu Dawud, and it will also come later at 8035, from Abu Kamil, with this isnad. It will also come at 8514 from Affan, and at 8623 from Hasan, both of them from Hammad, with the same wording.Tayalisi narrated it (2534) from Umara bin Zazan Saydalani, from Ali bin Hakam Banani, with this isnad, similarly. Likewise, Tirmidhi narrated it (3:370), and Ibn Majah (261), and Ibn Abdul-Barr (5:1), all of them through Umara bin Zazan. It will also come at 10425 from Ibn Numayr, from Umara. It was also narrated by Hajjaj bin Artah, from Ata bin Abu Rabah, from Abu Hurairah, with similar wording, and it will come through Hajjaj at 7930, 10492, and 10605. It was also narrated by Layth bin Abu Salim, from Ata, with similar wording, in Ibn Abdul-Barr (5:1).Abdul-Warith bin Saeed made a mistake when he narrated this hadith from Ali bin Hakam, adding an unnamed man to the isnad. Hakim narrated it in Mustadrak (1:101), through Muslim bin Ibrahim, and Ibn Abdul-Barr narrated it in Jami Bayan Ilm (4:1), through Musaddad, both of them from Abdul-Warith, from Ali bin Hakam, from a man, from Ata, from Abu Hurairah.We are certain that the error of adding the unnamed man came from Abdul-Warith, because two reliable narrators transmitted it from him with this addition, and it is unlikely that the mistake would come from both of them rather than from him. Also, two reliable narrators transmitted it from Ali bin Hakam, namely Hammad bin Salama and Umara bin Zazan, as we explained before, and they did not mention this unnamed man between Ali bin Hakam and Ata. Two are closer to accurate preservation and more deserving of preference than one.Moreover, there is disagreement about Abdul-Warith himself regarding this unnamed man he added, as to where his place is in the isnad. Hakim also narrated it, through Azhar bin Marwan, who said, "Abdul-Warith bin Saeed narrated to us. Ali bin Hakam narrated to us, from Ata, from a man, from Abu Hurairah." So he placed the unnamed man between Ata and Abu Hurairah.Hakim related, regarding this, an interesting and noteworthy story between himself and his teacher, the great hadith master Abu Ali Husayn bin Ali Nisaburi, which is decisive proof of the soundness of the hadith. He first narrated it (1:101) through Muhammad bin Thawr Sanani, who is a well-known reliable narrator, whom Abu Zura testified to be better than Abdul-Razzaq. Muhammad bin Thawr said, "Ibn Jurayj narrated to us, saying, 'Amash came to Ata and asked him about a hadith, so he related it to him. We said to him, "Are you relating this from him, though he is an Iraqi?" He said, "It is because I heard Abu Hurairah relating from the Prophet ﷺ, who said, 'Whoever is asked about knowledge and conceals it will be brought on the Day of Resurrection bridled with a bridle of fire.'"'"Then Hakim said, "This is a hadith that people have transmitted through many isnads, which are collected and studied together. This isnad is sahih according to the criteria of the two Shaykhs, though they did not include it. I discussed this chapter with our teacher, Abu Ali the hadith master, then I asked him, 'Is any of these isnads sound from Ata?' He said, 'No.' I said, 'Why?' He said, 'Because Ata did not hear it from Abu Hurairah.'"Then Hakim narrated, from his teacher Abu Ali, the report of Azhar bin Marwan, which we mentioned, in which the unnamed man is placed between Ata and Abu Hurairah. Then Hakim said, commenting on his teacher Abu Ali, "I said to him, 'Either Azhar bin Marwan made a mistake in it, or your teacher Ibn Ahmad Wasiti did, and an error from either of them is not unlikely.'"Then he related to his teacher Abu Ali the report of Muslim bin Ibrahim, which we mentioned earlier, from Abdul-Warith bin Saeed, in which the unnamed man is placed between Ali bin Hakam and Ata. Then Hakim said, "Abu Ali, meaning his teacher, the hadith master, approved of it and acknowledged it to me."Then, when I gathered the chapter, I found a group who mentioned in it that Ata had heard from Abu Hurairah.So the report of Hakim, and the report of his teacher Abu Ali, through Abdul-Warith, indicate that there was disagreement regarding Abdul-Warith about the unnamed man he added to the isnad, whether he is between Ata and Abu Hurairah, or between Ali bin Hakam and Ata. Perhaps these two also indicate that Abdul-Warith did not memorize this isnad well and was not precise about it. Moreover, two reliable narrators contradicted him, namely Hammad bin Salama and Umara bin Zazan, as we mentioned.Then all doubt about the soundness of the hadith was removed by Ibn Jurayj's narration of it from Ata, in the context of a specific incident, in which Ibn Jurayj asked him, "How can Amash relate this hadith when he is from the people of Iraq?" So he answered him with this hadith, and stated clearly that he had heard it from Abu Hurairah.This isnad, meaning the isnad of the hadith of Ibn Jurayj from Ata, as found in Hakim, is a sahih isnad according to the criteria of the two Shaykhs, as Hakim said, and as Dhahabi confirmed.