John 7:1-24, Jesus teaching at the feast of tabernacles.
Technically it was Jesus’ half brothers, since Jesus was adopted by Joseph. An alternate explanation, favored by Catholics is that it was his cousins, or sons of Joseph from a previous marriage.
From Leviticus 12:3 And in the eighth day the flesh of his foreskin shall be circumcised. It was an absolute command, and had to be performed on the eighth day, even if that day was a Sabbath.