Devibhagavatapurana 2.4.9

2.4.9

sūta uvāca |
rājā tāṃ nābhijānāti gaṅgeyamiti niścitam |
mahābhiṣaṃ samutpannaṃ nṛpaṃ jānāti jāhnavī ||

Sûta said:-- The king S’antanu could not recognise the lady to be Gangâ; but Gangâ knew that he is the king Mahâbhisa and is born as S’antanu. Hearing the above words of the king, Gangâ, out of her previous affections, spoke out to the king, smiling:-- “O king! I know that you are the son of the king Pratîpa. Behold! Though it is inevitable that woman will get their husbands, yet who is that beautiful lady that does not husband according to her liking and qualifications? But I can take you as my husband, if you make a certain promise to me. Hear my resolve afterwards I will marry you. O king! Whatever I will do, be it good or bad, auspicious or inauspicious, you must not hinder or interrupt me nor ever say that is not to your liking and satisfaction. Whenever you will break this my resolve, I will instantly quit you and go to another place wherever I like. The king S’antanu, then, said:-- “Well! That will be” and promised to the above effect; then Gangâ Devî recollected within herself Vasus' words and thought of the attachment of the king Mahâbhisa and accepted S’antanu as her husband. Thus married to the king S’antanu, the beautiful Gangâ in human form went to his abode. The king, on having got possession of her, began to enjoy in pleasant gardens. The lady, too, appreciated his mental feelings and began to serve him to his satisfaction. Thus many years elapsed in lovely enjoyments and intercourses between the couple who looked like Indra and his pair Sachî; and they did not feel at all how the time passed. The lady endowed with all qualities and the clever king, well-versed in the art of loving, began to enjoy incessantly like Laksmî and Nârâyana, in their divine palace.
Thus many years passed when the lovely eyed lady became pregnant of the king S’antanu's sperm and, in due time, gave birth to a son who was a Vasu. No sooner the son was born than Gangâ Devî threw it in the waters of the Ganges. Thus the second, third, fourth, fifth, sixth and seventh sons were threwn successively on the waters. Then the king became very anxious and thought within himself:-- “What am I to do now? How my family be preserved? This my wife, incarnate of sin, has killed my seven sons; if I now desist her, she will instantly leave me and go away. Now this is the eighth pregnancy as desired by me. Now if I do not interrupt her, she will certainly throw my son in the Ganges. Whether a son will be born again or not is doubtful; and even if that be born, it is doubtful whether she will preserve that child; now what am I to do in this doubtful point? However I will try my best to continue the thread of my family line.”