I missed today's episode. They must have shown Krishna breaking his vow and Bhishma surrendering to him.
Krishna breaking his vow to uphold Bhishma's wish is mentioned in Srimad Bhagvatam.
sva-nigamam apahiiya mat-pratijiiam
rtam adhikartum avapluto rathastha?t
dhrta-ratha-carar-o 'bh )'ayiic caladgur
harir iva hantum ibhmh gatottar_iyaft
Fulfilling my desire and sacrificing His own promise, He got down from the chariot, took up its wheel, and ran towards me hurriedly, just like a lion goes to kill an elephant. He even dropped His outer garment on the way.
Canto 1, Chapter 9
Interestingly, the lion-elephant finds a mention in Mahabharata too.