Al-Kāfi - Volume 4 > Taqsir (Trimming something from One’s Hair or Nails After Completing Sa‘y) of One Who Is for al-Hajj al-Tamattu‘ (advantageous) and Coming Out of the State of Ihram
Hadith #5

5ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ أَسْلَمَ قَالَ لَمَّا أَرَادَ أَبُو جَعْفَرٍ يَعْنِي ابْنَ الرِّضَا (عَلَيْهِ السَّلاَم) أَنْ يُقَصِّرَ مِنْ شَعْرِهِ لِلْعُمْرَةِ أَرَادَ الْحَجَّامُ أَنْ يَأْخُذَ مِنْ جَوَانِبِ الرَّأْسِ فَقَالَ لَهُ ابْدَأْ بِالنَّاصِيَةِ فَبَدَأَ بِهَا.

5. A number of our people have narrated from Ahmad ibn Muhammad from al-FIusayn ibn Aslam who has said the following: “When abu Ja‘far, ibn al-Rida’, ‘Alayhi al-Salam, wanted to do Taqsir (cutting some hair or finger nails and so on) after al-‘Umrah, the barber wanted to take from the sides of his head but he (the Imam) said, ‘Take from the side of the forehead and the barber did accordingly.’”