Kamasutra 2.1.21

2.1.21

tac ca na. sāmānye 'pi bhrānti-saṃskāre kulāla-cakrasya bhramarakasya vā bhrāntāv eva vartamānasya prārambhe manda-vegatā tataś ca krameṇa pūraṇaṃ vegasyety upapadyate. dhātu-kṣayāc ca virāmābhīpseti. tasmād an:ākṣepaḥ.

This objection, however, does not hold good, for even in ordinary things that revolve with great force, such as a potter's wheel, or a top, we find that the motion at first is slow, but by degrees it becomes very rapid. In the same way the passion of the woman having gradually increased, she has a desire to discontinue coition, when all the semen has fallen away. And there is a verse with regard to this as follows:—