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The Great Purana, Uttara Purana
"Do not become like Ashanighosh, who has been defeated. Do not think that I am saying this out of fear of being a co-wife. Accept my words as proof and abandon your attachment to Sita." Thus spoke Mandodari to Ravana. Ravana was unable to answer her words and, filled with anger, returned to the city, saying, "She can only be abandoned with her life."
Meanwhile, Mandodari, consumed by grief for her abandoned daughter, said to Sita in private, "My mind believes that you, my daughter, have come here to cause strife. You were buried in the earth by the order of the knower of destiny. Blessed one, you have been brought here by the wicked fate."
"It is true that the will of fate is rarely violated in this world. I do not know if you are related to me in this birth or in a previous birth. I do not know why my love for you is growing today when I see you. O lotus-eyed one, it is possible that I am your mother and you are my daughter, and you understand this too. But the king of the Vidyadharas wants to make you my co-wife. Therefore, my child, even if you have to face death, do not fulfill his desire, do not act according to his wishes."
Thus speaking, Mandodari became very eager. Milk filled her breasts, and her breasts seemed to bend down to anoint Sita. Her throat choked, tears of affection flowed from her eyes, and her lotus-like face was stained with the soot of grief.
Seeing all this, Sita felt as if she had come to her mother. Her heart became soft and her eyes filled with tears.
Knowing her intention, Mandodari, the best of Ravana's wives, said, "Mother, if you wish to accomplish your task well, I beg you with folded hands, take food. The body is the means of everything, and food is the means of the body."
Wise men say, "Where there is no tree, there will be no flowers." Similarly, while the body remains, you will be able to see your lord Ramachandra. If his vision is not attainable, then perform great penance with this body. If you do not accept my words, then I myself will be your food.