A Little Biblical Commentary:

Genesis 17:23--On that same day, Abraham obeyed God and circumsised his son Ishmael, and all the other males in his household, including the slaves born in his home, and those he had bought.

Man. That had to be a rough and confusing day to those males within the household not recieving the Word of God direct from the Maker hisself. That's what you call a leap of faith.