Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Mu'adh (may Allah be pleased with him) that when the Holy Prophet (peace and blessings be upon him) sent him to Yemen as a judge, he asked him: "How will you judge?" Hazrat Mu'adh (may Allah be pleased with him) replied, "I will judge according to the Book of Allah." The Prophet (peace and blessings be upon him) said, "If a matter arises that is not in the Book of Allah?" Hazrat Mu'adh replied, "I will judge according to the Sunnah of the Messenger of Allah (peace and blessings be upon him)." The Prophet (peace and blessings be upon him) said, "If that matter is not in the Sunnah of the Messenger of Allah (peace and blessings be upon him) either?" Hazrat Mu'adh (may Allah be pleased with him) replied, "I will judge according to my own opinion." The Prophet (peace and blessings be upon him) said, "All praise is due to Allah who has granted the messenger of the Messenger of Allah the ability to do this."

It is narrated from Hazrat Muhammad bin Ubaidullah that when the Holy Prophet (peace be upon him) sent Hazrat Mu'adh (may Allah be pleased with him) to Yemen as a judge, he said, "O Mu'adh! How will you judge?" Hazrat Mu'adh replied, "I will judge according to the Book of Allah." The Prophet (peace be upon him) said, "If a matter arises that is not in the Qur'an?" Hazrat Mu'adh replied, "I will judge according to the decision of the Messenger (peace be upon him)." The Holy Prophet (peace be upon him) said, "If a matter arises that is neither in the Qur'an nor has the Prophet (peace be upon him) decided about it, nor is there a decision from the righteous predecessors regarding it?" Hazrat Mu'adh (may Allah be pleased with him) replied, "I will do my best and make a correct decision based on my own effort and opinion." The Noble Prophet (peace be upon him) said, "All praise is due to Allah who has granted the messenger of the Messenger of Allah (peace be upon him) the ability to decide according to what pleases the Messenger of Allah (peace be upon him)."

Hazrat Shurayh narrates that Hazrat Umar (may Allah be pleased with him) wrote to him: If there is a matter that is found in the Qur'an, then decide according to it, and do not let people put you to trial regarding it. And if a matter arises that is not in the Qur'an, then look to the Sunnah of the Noble Prophet (peace and blessings be upon him) and decide according to it. And if there is a matter that is neither in the Qur'an nor in the Sunnah of the Messenger of Allah (peace and blessings be upon him), then see what the people have agreed upon and adopt that decision. And if a matter arises that is neither in the Qur'an, nor in the Sunnah of the Messenger of Allah, nor has anyone before you given a decision about it, then choose one of the two options: if you wish to exercise ijtihad with your own opinion and go ahead of the people, you may do so, and if you wish to hold yourself back, you may also do so. I consider it better for you to hold yourself back.

It is narrated from Hazrat Abdur Rahman bin Yazid that one day people came to Hazrat Abdullah, and he said: O people! Indeed, there was a time upon us when neither did we pass judgments nor were we present at the place of judgment. Then Allah Almighty destined the matter of leadership for us, as you see. So after today, whoever among you is presented with the responsibility of judgment, he should judge according to the Qur'an, and if a matter arises which is not in the Qur'an, then he should judge according to the Sunnah of the Noble Prophet (peace and blessings be upon him), and if a matter arises which is neither in the Qur'an nor in the Hadith, then judge according to what the righteous have decided, and if there is a matter which is neither in the Qur'an nor in the Sunnah, and the righteous have also not given a decision regarding it, then exercise ijtihad according to your own opinion, and he should not say: I fear, I fear. Surely, the lawful is clear and the unlawful is clear, and between them are some doubtful matters, so leave that which puts you in doubt and choose that which is certain.

It is also narrated in the same manner from Hazrat Abdullah.

It is narrated from Hazrat Abdullah in the same manner, but with this addition: if any matter arises which he does not know, he should admit it (i.e., acknowledge that he does not know about this matter) and should not feel ashamed.

When something was asked of Hazrat Ibn Abbas (may Allah be pleased with them both) and it was found in the Qur'an, he would inform about it; and if it was not in the Qur'an but was found in the Hadith of the Messenger, he would inform about that; and if it was not found in either, he would look into the statements of Hazrat Abu Bakr and Umar (may Allah be pleased with them both); and if it was not found there either, then he would exercise his own judgment (ijtihad).