A Commandment That Overrides a Prohibition
Why did Abraham our forefather not circumcise himself before he was commanded, seeing that he fulfilled the whole Torah before it was even given?
Rather, Abraham was not permitted to circumcise himself before being commanded to do so by G-d, because of the prohibition against shedding blood, for the Torah forbids a person to shed his own blood. Only after he was commanded regarding the commandment of circumcision did the commandment of circumcision override the prohibition against shedding one's own blood.
(the Rebbe)