tayor eko balabhadro babhūva yo 'sau śvetas tasya devasya keśaḥ kṛṣṇo dvitīyaḥ keśavaḥ saṁbabhūva keśaḥ yo 'sau varṇataḥ kṛṣṇa uktaḥ

Thus in Srimad-Bhagavatam, Visnu Purana and Mahabharata there are references to Krsna and Balarama being incarnations of a black hair and a white hair. It is stated that Lord Visnu snatched two hairs-one white and one black-from His head. These two hairs entered the wombs of Rohini and Devaki, members of the Yadu dynasty. Balarama was born from Rohini, and Krsna was born of Devaki. Thus Balarama appeared from the first hair, and Krsna appeared from the second hair. It was also foretold that all the asuras, who are enemies of the demigods, would be cut down by Lord Visnu by His white and black plenary expansions and that the Supreme Personality of Godhead would appear and perform wonderful activities. In this connection, one should see Laghu-bhagavatamrta, the chapter called Krsnamrta, verses 156-164. Srila Rupa Gosvami has refuted this argument about the hair incarnation, and his refutation is supported by Sri Baladeva Vidyabhusana's commentaries. This matter is further discussed in the Krsna-sandarbha (29) and in the commentary known as Sarva-samvadini, by Srila Jiva Gosvami.