Chapter on the Hajj of Children
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 3|Chapter 92
وَ رُوِيَ عَنْ عَلِيِّ بْنِ مَهْزِيَارَ عَنْ مُحَمَّدِ بْنِ اَلْفُضَيْلِ قَالَ: سَأَلْتُ أَبَا جَعْفَرٍ اَلثَّانِيَ عَنِ اَلصَّبِيِّ مَتَى يُحْرَمُ بِهِ قَالَ «إِذَا اِثَّغَرَ».
It was narrated from Ali ibn Mahziyar, from Muhammad ibn al-Fudhayl, who said: I asked Abu Ja'far al-Thani, Imam Muhammad al-Jawad عليه السلام about when a child should be entered into the state of Ihram. Imam عليه السلام said: "When they begin to grow teeth."
- Ṣaḥīḥ al-Faqīh