It is narrated from Qays that Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) was asked about Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), and he said: "He recited the Qur'an, then reflected deeply on its ambiguous (subtle) matters, and he held its lawful to be lawful and its unlawful to be unlawful." Then he was asked about Sayyiduna Ammar (may Allah be pleased with him), and he said: "He is a believer who forgets (the truth), but when he is reminded, he remembers." And when he was asked about Sayyiduna Hudhayfah (may Allah be pleased with him), he said: "He was the most knowledgeable of all people about the hypocrites." And the narrator mentioned the rest of the hadith.