Mbh 6.99.2a

“Hearing those copious lamentations of Duryodhana in the night, Bhishma regarded them, O king, as commands to himself. Filled with great grief and deprecating the status of servitude, Santanu’s son reflected for a long time, thinking of an encounter with Arjuna in battle. Understanding from signs that Ganga’s son had been thinking of that, Duryodhana, O king, commanding Dussasana, saying, ‘O Dussasana, let cars be quickly appointed for protecting Bhishma. Let all the two and twenty divisions (of our army) be urged on. That hath now come about which we had been thinking for a series of years, viz., the slaughter of the Pandavas with all their troops and the acquisition (by ourselves) of the kingdom. In this matter, I think, the protection of Bhishma is our foremost duty. Protected by us, he will protect us and slay the Parthas in battle. Of cleansed soul, he said unto me,--“I will not slay Sikhandini. He was a female before, O king, and, therefore, should be avoided by me in battle. The world knoweth, O thou of mighty arms, that from desire of doing good to my father, I formerly gave up a swelling kingdom. I will not, therefore, slay in battle, O foremost of men, any female or anybody that was a female before. This that I tell thee is true. This Sikhandin, O king, was first born a female. Thou hast heard that story. She was born as Sikhandini after the manner I told thee before the battle began. Taking her birth as a daughter she hath become a man. Indeed, she will fight with me, but I will never shoot my arrows at her. As regards all other Kshatriyas desirous of victory to the Pandavas, O sire, whom I may get within my reach on the field of battle, I will slay them.”--These were the words that Ganga’s son acquainted with the scriptures, that chief of Bharata’s race, said unto me. Therefore, with my whole soul I think that protecting the son of Ganga is our foremost duty. The very wolf may slay the lion left unprotected in the great forest.