Al-Kāfi

Hadith 141
circumcision
عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ أَبِي عَبْدِ اللَّهِ عَنْ أَبِيهِ عَنْ عَبْدِ اللَّهِ بْنِ الْمُغِيرَةِ عَمَّنْ ذَكَرَهُ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ الْمَوْلُودُ يُعَقُّ عَنْهُ وَ يُخْتَنُ لِسَبْعَةِ أَيَّامٍ .
9. A number of our people have narrated from Ahmad ibn abu ‘Abd Allah from his father from ‘Abd Allah ibn al-Mughirah from those whom he has mentioned who has said the following: “Abu ‘Abd Allah (a.s.), has said, ‘For a newborn ‘Aqiqah is offered on the seventh day and the child is circumcised.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī