Tirmidhi Book 15, Hadith 1327

حَدَّثَنَا هَنَّادٌ، حَدَّثَنَا وَكِيعٌ، عَنْ شُعْبَةَ، عَنْ أَبِي عَوْنٍ الثَّقَفِيِّ، عَنْ الْحَارِثِ بْنِ عَمْرٍو، عَنْ رِجَالٍ مِنْ أَصْحَابِ مُعَاذٍ، ‏‏‏‏‏‏أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بَعَثَ مُعَاذًا إِلَى الْيَمَنِ، ‏‏‏‏‏‏فَقَالَ:‏‏‏‏ كَيْفَ تَقْضِي ؟ فَقَالَ:‏‏‏‏ أَقْضِي بِمَا فِي كِتَابِ اللَّهِ. قَالَ:‏‏‏‏ فَإِنْ لَمْ يَكُنْ فِي كِتَابِ اللَّهِ ؟ قَالَ:‏‏‏‏ فَبِسُنَّةِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ. قَالَ:‏‏‏‏ فَإِنْ لَمْ يَكُنْ فِي سُنَّةِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ؟ قَالَ:‏‏‏‏ أَجْتَهِدُ رَأْيِي، ‏‏‏‏‏‏قَالَ:‏‏‏‏ الْحَمْدُ لِلَّهِ الَّذِي وَفَّقَ رَسُولَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ .

Some men who were companions of Mu'adh narrated from Mu'adh that the Messenger of Allah (ﷺ) sent Mu'adh to Yemen, so he (ﷺ) said: How will you judge? He said: I will judge according to what is in Allah's Book. He said: If it is not in Allah's Book ? He said: Then with the Sunnah of the Messenger of Allah (ﷺ). He said: If it is not in the Sunnah of Messenger of Allah (ﷺ)? He said: I will give in my view. He said: All praise is due to Allah, the One Who made the messenger of the Messenger of Allah suitable.