Valmiki Ramayana Ayodhya Kanda Sarga 110 Shloka 18

अस्य his, द्वे भार्ये two wives, गर्भिण्यौ बभूवतुः became pregnant, इति like this, श्रुतिः it is said, एका one, गर्भविनाशाय to destroy the embryo, सपत्नयै to her cowife, गरलम् poison, ददौ gave.

Both his wives became pregnant. It is said that one of them gave the other poison (with the motive) to destroy the embryo.