Every father has to fulfill HaShem's Covenant to circumcise his son on the eighth day, someone qualified repesentative to do this on his behalf. This ritual is known as the Brit, which means Covenant and the word for circumcision is Milah.
The Bris Milah means Covenant of circumcision and this ritual must been done by a Mohel who is qualifiedto perform the circumcision and also is trained in techniques of surgical hygienes, from a religious point of view it is not justified having a surgeon perform the circumcision whil a Rabbi recites the blessing.
As said before the Bris has to take place on the eighth day , even when it is Shabbat or Yom Kippur, of course it depends on the day the child is born, lets say a child is born after nightfall on a tuesday then the Bris will the Bris will take place on the following wednesday, always during daytime and preferable in the morning.
When a child is sick or born prematurely, only then and from a medical point of view it will be dangerous, then the bris will be postponed till a later date, Shluchan Aruch orders caution and says the Brit should be delayed.
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This is My Covenant which you shall keep, every male among you shall be circumcised, that shall be the sign of the Covenant between Me and you. At the age of eight days every male among you shall be circumcised throughout the generations, and the un-circumcised male shall be cut of from his people, he has broken My Covenant.
🔸️Bereishis 17: 10~ 14🔸️