Ramayana
एवमुक्तो दशग्रीवः प्रत्युवाच विनीतवत् । स्नुषा ऽस्मि यदवोचस्त्वमेकपत्नीष्वयं क्रमः । देवलोकस्थितिरियं सुराणां शाश्वती मता ॥ 7-26-40 ॥
Addressed thus, the ten-necked Ravana replied with feigned humility: "As for what you have said, that you are a daughter-in-law to me, that rule applies only to women who have but one husband; this is held to be the eternal custom of the gods in the world of the gods."
english translation