http://revach.net/article.php?id=601

Section: Parshas HaShavua   Category: Numbers & Letters
Parshas Devarim: Og Melech HaBashan and His Bris Milah

The Zohar says that Og Melech HaBashan had a Bris Milah with Avrohom serving as the Mohel. Because of this z'chus says the Alshich, Moshe Rabbeinu was scared to go fight with him.

This is seen in the pasuk in Devarim (3:2) where Moshe says that Hashem told him. "Al Tirah Oisoi; Do not fear him, Ki BiYadcha Nasati Oisoi; Because in your hands I will deliver him." Why does it say twice "oisoi"? The Alshich says in the first "oisoi" if you put the "vuv" in the middle instead of the end, it reads "ois" another word for Bris Milah. Hashem is saying that Moshe should not fear Og's z'chus of Bris Milah. Why? Because you have a greater z'chus. Moshe was born with a Bris Milah and he was the mohel for all the "Yotzai Mitzrayim". Therefore Hashem says to Moshe. "I will deliver Og into your hands and only you have the power to slay Og, not the Bnei Yisroel." Moshe ultimately killed Og himself.