VOL. 6, CHAPTER 9, VERSE 9.
SHASHTAMA SKANDHAM, ADHYaYA 9 SLoKA 9.
SASvata kAma varENAmhas
turIyam jagruhu strIyaha
rajO rUpENa tAsv amho
mAsi mAsi pradrusyatE.
CONTEXT AND GIST
The chief of demy Gods Indra killed the demon Vritra, who was said to be a Brahmin. Killing a Brahmin was said to be a great sin. Indra wanted to distribute the burden of his sin to other.
Women were one of the recipients of the sin. There was a trade. Indra gave a boon of constant sexual desires for women. In exchange, women had to accept the painful monthly discharge as the sin.
We can wonder how the priests were able to create a cock and bull story, for a biological phenomenon like monthly menstruation.