Mbh 1.169.2c

Enmity with Drona burneth my heart; it behoveth thee therefore to cool that heart of mine. Foremost of those conversant with the Vedas, Drona is also skilled in the Brahma weapon and for this, Drona hath overcome me in a contest arising from (impaired) friendship. Gifted with great intelligence, the son of Bharadwaja is (now) the chief preceptor of the Kurus. There is no Kshatriya in this world superior to him. His bow is full six cubits long and looks formidable, and his shafts are capable of slaying every living being. That great bowman, the high-souled son of Bharadwaja, habited as a Brahmana, is destroying the Kshatriya power all over the earth. Indeed, he is like a second Jamadagnya intended for the extermination of the Kshatriya race. There is no man on earth who can overcome the terrible force of his weapons. Like a blazing fire fed with clarified butter, Drona, possessed of Brahma might and uniting it with Kshatriya might, consumeth every antagonist in battle. But (thy) Brahma force is greater in itself than (Drona’s) Brahma force united with Kshatriya might. Therefore, as I am inferior (to Drona) in consequence of my possession of Kshatriya might alone, I solicit the aid of thy Brahma force, having obtained thee so superior to Drona in knowledge of Brahma. O Yaja, perform that sacrifice by means of which I may obtain a son invincible in battle and capable of slaying Drona. Ready am I to give thee ten thousand kine.’ Hearing these words of Drupada, Yaja said, ‘So be it.’ Yaja then began to recollect the various ceremonies appertaining to the particular sacrifice. And knowing the affair to be a very grave one, he asked the assistance of Upayaja who coveted nothing. Then Yaja promised to perform the sacrifice for the destruction of Drona. Then the great ascetic Upayaja spoke unto king Drupada of everything required for the grand sacrifice (by aid of fire) from which the king was to obtain offspring.