Valmiki Ramayana Ayodhya Kanda Sarga 9 Shloka 4
Original Shlokaएवमुक्ता तया देव्या मन्थरा पापदर्शिनी। रामार्थमुपहिंसन्ती कैकेयीमिदमब्रवीत्।।2.9.4।।
1 source checked for this shloka
तया देव्या by that queen, एवम् thus, उक्ता having been addressed, पापदर्शिनी evilminded रामार्थम् Rama's interests, उपहिंसन्ती destroying, कैकेयीम् to Kaikeyi, इदम् this, अब्रवीत् said.
Thus addressed by queen Kaikeyi, that evil minded Manthara said this to Kaikeyi in order to spoil the interest of Rama: