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.