Harith bin Zuhair said: I think that Abdullah bin Mas'ud (may Allah be pleased with him) said: There was a time upon us when we did not ask any questions, as if we did not even exist in that era, and Allah Almighty decreed that now I have reached the state as you see. So when you are asked about any matter, seek it in the Book of Allah; if you do not find it in the Book of Allah, then seek it in the Sunnah of the Messenger of Allah (peace and blessings be upon him); and if you do not find it in the Sunnah of the Messenger, then look at what the Muslims have agreed upon; and if you do not find the matter in the consensus of the Muslims, then reflect and exercise ijtihad, and do not say, "I fear" or "I am afraid." Surely, the lawful is clear and the unlawful is also clear, and between the two are some doubtful matters, so leave that which is doubtful and adopt that which is certain.

Abdur Rahman bin Yazid also narrated the aforementioned narration from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him).

Qasim bin Abdur Rahman narrated from his father, who narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) in the same manner.

A‘mash (Sulaiman bin Mehran) narrated that Sayyiduna Abdullah bin Mas‘ud (may Allah be pleased with him) said: O people! You will invent new things and new things will be invented for you, so when you see any new matter, hold fast to the original way. The narrator Hafs bin Ghiyath said: Previously, I used to narrate this athar from Habib (bin Thabit) from Abu Abdur Rahman al-Sulami, but then I became doubtful about it, (and he narrated this report from A‘mash from Sayyiduna Abdullah bin Mas‘ud (may Allah be pleased with him), in which there is a break in the chain).

Imam Muhammad bin Sirin, may Allah have mercy on him, said that Sayyiduna Umar, may Allah be pleased with him, said to Sayyiduna Abdullah bin Mas'ud, may Allah be pleased with him: "I have heard that you give fatwas even though you are not the leader. Leave each matter to the one it is suited for."

Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Any person who answers whatever he is asked is insane.

Sayyiduna Hudhayfah (may Allah be pleased with him) said: Three types of people can give fatwa: the Imam, or the ruler of the government, or the person who is knowledgeable about the abrogating and abrogated verses of the Qur'an. The people asked: Who can such a person be? He said: Either Sayyiduna Umar ibn al-Khattab (may Allah be pleased with him), or a foolish ignoramus who takes it upon himself.

Sayyiduna Hudhayfah (may Allah be pleased with him) said: One of three can give a fatwa. The one who has knowledge of the abrogating and abrogated. The people asked: Who is such a person? He replied: Sayyiduna Umar ibn al-Khattab (may Allah be pleased with him), or such a leader who has no choice but to give a fatwa, or a foolish person who takes it upon himself. Then Muhammad ibn Sirin (may Allah have mercy on him) said: I am not among those two (i.e., the ruler or governor), and I hope not to become the third (the foolish self-imposer) either.

Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Whoever among you has knowledge should make it apparent, and whoever does not have knowledge should say about what he does not know: «لا أعلم» (that is, "I do not know"), because if a scholar is asked about something he does not know, he should say «الله أعلم» , just as Allah Almighty said to His Messenger (peace and blessings be upon him): "Say: I do not ask you for any reward for it, nor am I one of those who pretend." [سورة ص: 86/38]

It is narrated from Abu al-Muhallab that Sayyiduna Abu Musa Ash'ari (may Allah be pleased with him) said during a sermon: Whoever has knowledge should teach the people, and beware, whoever does not have knowledge about something should not say anything regarding it. If he does so, he will go out of the religion and will be among those who are pretentious.