Sahih Muslim Book - 0, Hadith - 22

حَدَّثَنَا دَاوُدُ بْنُ عَمْرٍو الضَّبِّيُّ حَدَّثَنَا نَافِعُ بْنُ عُمَرَ عَنْ ابْنِ أَبِي مُلَيْكَةَ قَالَ كَتَبْتُ إِلَى ابْنِ عَبَّاسٍ أَسْأَلُهُ أَنْ يَكْتُبَ لِي كِتَابًا وَيُخْفِي عَنِّي فَقَالَ وَلَدٌ نَاصِحٌ أَنَا أَخْتَارُ لَهُ الْأُمُورَ اخْتِيَارًا وَأُخْفِي عَنْهُ قَالَ فَدَعَا بِقَضَاءِ عَلِيٍّ فَجَعَلَ يَكْتُبُ مِنْهُ أَشْيَاءَ وَيَمُرُّ بِهِ الشَّيْءُ فَيَقُولُ وَاللَّهِ مَا قَضَى بِهَذَا عَلِيٌّ إِلَّا أَنْ يَكُونَ ضَلَّ

It was narrated that Ibn Abi Mulaikah said, "I wrote to Ibn Abbas asking him to write something for me, but to be selective. He said, 'A sincere boy, I will choose for him and be selective.' He called for a record of judgements passed by Ali, and he started to write down some of them and he would come across some things and say, 'By Allah, Ali would never have passed such a judgement unless he got it wrong.'"