Al-Kāfi 6, narration 135

Translation

3. Muhammad ibn Yahya and Muhammad ibn ‘Abd Allah have narrated from ‘Abd Allah ibn Ja‘far who has said the following: “I once wrote to abu Muhammad (a.s.), that it is narrated from the two truthful Imam, ‘Alayhim al-Salam, who have said, ’Circumcise your children on the seventh day from their birth; the earth cries before Allah because of the urine of an uncircumcised person.’ I pray to Allah to keep my soul in service for your cause, people performing circumcision in our city are not very knowledgeable and they do not do it on the seventh day but there is a Jewish person; if it is permissible for a Jewish person to circumcise children of Muslims or not by the will of Allah. He (the Imam) signed the answer that said, ’It is of Sunnah to circumcise on the seventh day, so do not oppose the Sunnah by the will of Allah.’”

Translation: Muhammad Sarwar — published with the edition, reproduced verbatim.