SB 10.74.43
tavad utthaya bhagavan
svan nivarya svayam rusa
sirah ksuranta-cakrena
jahara patato ripoh
Translation:
At that point the Supreme Lord stood up and checked His devotees. He then angrily sent forth His razor-sharp disc and severed the head of His enemy as he was attacking.
Purport:
Srila Visvanatha Cakravarti Thakura explains the Lord’s action as follows: If Lord Krsna had done nothing, there probably would have been a savage fight on the sacrificial grounds, and thus the whole ceremony would have been drenched in blood, spoiling the sanctified atmosphere. Therefore, in order to protect the Rajasuya sacrifice of Krsna’s beloved devotee Yudhisthira, the Lord immediately severed Sisupala’s head with His razor-sharp disc in such a way that not a drop of blood fell within the sacrificial grounds.