(15) The Chapters On Judgements From The Messenger of Allah
كتاب الأحكام عن رسول الله صلى الله عليه وسلم
(1) Chapter: What Has Been Related From The Messenger of Allah About The Judge
(1) باب مَا جَاءَ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فِي الْقَاضِي ‏
Jami` at-Tirmidhi 1323 
Anas bin Malik narrated that the Messenger of Allah (sallAllahu Alayhi wa sallam) said:
"Whoever asks for a position as a judge, then he left on his own. And whoever is forced onto it, Allah sends an angel down to him so that he can be correct." (Daif)
حَدَّثَنَا هَنَّادٌ، حَدَّثَنَا وَكِيعٌ، عَنْ إِسْرَائِيلَ، عَنْ عَبْدِ الأَعْلَى، عَنْ بِلاَلِ بْنِ أَبِي مُوسَى، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ سَأَلَ الْقَضَاءَ وُكِلَ إِلَى نَفْسِهِ وَمَنْ أُجْبِرَ عَلَيْهِ يُنْزِلُ اللَّهُ عَلَيْهِ مَلَكًا فَيُسَدِّدُهُ ‏"‏ ‏.‏
Reference : Jami` at-Tirmidhi 1323
In-book reference : Book 15, Hadith 3
English translation : Vol. 3, Book 13, Hadith 1323