Valmiki Ramayana Ayodhya Kanda Sarga 9 Shloka 48
Original Shlokaजात्येन च सुवर्णेन सुनिष्टप्तेन मन्थरे।।2.9.48।। लब्धार्था च प्रतीता च लेपयिष्यामि ते स्थगु।
1 source checked for this shloka
मन्थरे O Manthara, लब्धार्था च after accomplishsing the objective, प्रतीता च also satisfied, जात्येन belonging to the best , सुनिष्टप्तेन highly refined, सुवर्णेन with gold, ते स्थगु your hump, लेपयिष्यामि will smear.
O Manthara, when my objective is accomplished and I am fully satisfied, I will smear your hump with the best of refined liquid gold.