Bhagavatapurana 3.12.51

3.12.51

na hy edhante prajā nūnaṃ daivam atra vighātakam /
evaṃ yukta-kṛtas tasya daivaṃ cāvekṣatas tadā //

51 & 52. While Brahma was thus doing what was proper and looking forward to the Providence, his form became divided into two and on this account he is called Kaya. And from the two divisions of that form a male and a female were produced.