It is narrated from Ibn Jurayj that Imam al-A'mash came to Ata (bin Abi Rabah) and asked him about a hadith, and he narrated it to him. We said to Ata: "You narrate this hadith to him even though he is an Iraqi?" (At that time there was rivalry between the scholars of Makkah and Iraq.) Ata said: "Because I heard Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrate this hadith from the Messenger of Allah (peace and blessings be upon him): 'Whoever is asked about some knowledge (which people need) and conceals it, will be brought on the Day of Resurrection bridled with a bridle of fire.'" This is a hadith that is widely known among people through many different chains, and this chain is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.