Mu'adh b. Jabal told that when Allah's Messenger ﷺ sent him to the Yemen he asked him how he would judge when the occasion arose, and he replied that he would judge in accordance with Allah’s Book. He asked what he would do if he could not find guidance in Allah’s Book, and he replied that he would act in accordance with Allah's Messenger ﷺ’s sunnah. He asked what he would do if he could find no guidance in Allah's Messenger ﷺ’s sunnah, and he replied that he would do his best to form an opinion and spare no pains. Allah's Messenger ﷺ then tapped him on the breast and said, “Praise be to Allah who has disposed His Messenger’s Messenger to something with which Allah's Messenger ﷺ is pleased!" Tirmidhi, Abu Dawud and Darimi transmitted it.