We all know stories about Bhishma pratigya, but little do we know about him holding his Guru, bhagwan Parshurama for twenty two days. Yes, this is true, there was a battle between these great warriors that ended in a stalemate.
The story goes like this, after rejected by her lover, Amba reached to Parshurama and requested him to teach Bhishma a lesson. Parshurama, who also was the teacher of Bhishma, decided to fight him in order to have justice for Amba. The fight ensued for a long time and nobody could be beaten. Reason, Parshurama was akhand chiranjeevi, means one who could not die and Bhishma had a boon from his father, Shantanu, that he would be able to choose the time of his death.