Chāndogya Upaniṣad 2.13.1

2.13.1

upamantrayate sa (S )kāraḥ \
jñapayate sa prastāvaḥ \
striyā saha śete sa udgīthaḥ \
(S ) śete sa pratihāraḥ \
kālaṃ gacchati tan nidhanam \
pāraṃ gacchati tan nidhanam \
etad vāmadevyaṃ mithune protam \\213.1\

1. One summons—that is a Hiṅkāra. He makes request—that is a Prastāva. Together with the woman he lies down—that is an Udgītha. He lies upon the woman—that is a Pratihāra. He comes to the end—that is a Nidhana. He comes to the finish—that is a Nidhana. This is the Vāmadevya Sāman as woven upon copulation.