Exodus 4:24

And it came to pass by the way in the inn that the Lord met him, and sought to kill him. In the place where Moses and his family encamped for the night while on the journey, the Lord threatened to take his life by a sudden disease, because he had neglected to circumcise his second son, Eliezer. Circumcision was the sign of the covenant between God and His people, and could not be omitted without grave consequences.