SB 3.12.52

evaṁ yukta-kṛtas tasya
 daivaṁ cāvekṣatas tadā
kasya rūpam abhūd dvedhā
 yat kāyam abhicakṣate
evam — thus; yukta — contemplating; kṛtaḥ — while doing so; tasya — his; daivam — supernatural power; ca — also; avekṣataḥ — observing; tadā — at that time; kasya — of Brahmā; rūpam — form; abhūt — became manifested; dvedhā — twofold; yat — which is; kāyam — his body; abhicakṣate — is said to be.
While he was thus absorbed in contemplation and was observing the supernatural power, two other forms were generated from his body. They are still celebrated as the body of Brahmā.

Two bodies came out from the body of Brahmā. One had a mustache, and the other had swollen breasts. No one can explain the source of their manifestation, and therefore until today they are known as the kāyam, or the body of Brahmā, with no indication of their relationship as his son or daughter.