Kamasutra 2.1.20

2.1.20

tatraitat syāt ṇ sātatyena rasa-prāptāv ārambha-kāle madhyastha-cittatā nāti:sahiṣṇutā ca. tataḥ krameṇādhiko rāga-yogaḥ śarīre nir:apekṣatvam ante ca virāmābhīpsety etad upapannam iti.

To this there is an objection. In the beginning of coition the passion of the woman is middling, and she cannot bear the vigorous thrusts of her lover, but by degrees her passion increases until she ceases to think about her body, and then finally she wishes to stop from further coition.