Sunan an-Nasa'i 5212
It was narrated that 'Ali said:
"The Messenger of Allah [SAW] said to me: 'Say: O Allah, guide me and make me steadfast,' and he forbade me to put a ring on this one and this one" - and Bishr (one of the narrators) pointed to his forefinger and middle finger. And 'Asim said: "One of the two of them."
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا بِشْرٌ، قَالَ حَدَّثَنَا عَاصِمُ بْنُ كُلَيْبٍ، عَنْ أَبِي بُرْدَةَ، عَنْ عَلِيٍّ، قَالَ قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ قُلِ اللَّهُمَّ اهْدِنِي وَسَدِّدْنِي ‏"‏ ‏.‏ وَنَهَانِي أَنْ أَضَعَ الْخَاتَمَ فِي هَذِهِ وَهَذِهِ وَأَشَارَ بِشْرٌ بِالسَّبَّابَةِ وَالْوُسْطَى ‏.‏ قَالَ وَقَالَ عَاصِمٌ أَحَدُهُمَا ‏.‏