Passage: Evidence suggests that circumcision was practiced in the Arabian Peninsula by the 4th millennium BCE, when the Sumerians and the Semites moved into the area that is modern-day Iraq.  The earliest historical record of circumcision comes from Egypt, in the form of an image of the circumcision of an adult carved into the tomb of Ankh-Mahor at Saqqara, dating to about 2400–2300 BCE.  Circumcision was done by the Egyptians possibly for hygienic reasons, but also was part of their obsession with purity and was associated with spiritual and intellectual development.  No well-accepted theory explains the significance of circumcision to the Egyptians, but it appears to have been endowed with great honor and importance as a rite of passage into adulthood, performed in a public ceremony emphasizing the continuation of family generations and fertility.  It may have been a mark of distinction for the elite:  the Egyptian Book of the Dead describes the sun god Ra as having circumcised himself.Though secular scholars consider the story to be literary and not historical, circumcision features prominently in the Hebrew Bible. The narrative in Genesis chapter 17 describes the circumcision of Abraham and his relatives and slaves. In the same chapter, Abraham's descendants are commanded to circumcise their sons on the eighth day of life as part of a covenant with God.

Question: On what day were the descendants ordered to do something to their sons?
eighth day