SB 9.24.34
amogham deva-sandarsam
adadhe tvayi catmajam
yonir yatha na dusyeta
kartaham te sumadhyame
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The sun-god said: O beautiful Prtha, your meeting with the demigods cannot be fruitless. Therefore, let me place my seed in your womb so that you may bear a son. I shall arrange to keep your virginity intact, since you are still an unmarried girl.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
According to Vedic civilization, if a girl gives birth to a child before she is married, no one will marry her. Therefore although the sun-god, after appearing before Prtha, wanted to give her a child, Prtha hesitated because she was still unmarried. To keep her virginity undisturbed, the sun-god arranged to give her a child that came from her ear, and therefore the child was known as Karna. The custom is that a girl should be married aksata-yoni, that is, with her virginity undisturbed. A girl should never bear a child before her marriage.