Valmiki Ramayana Kishkindha Kanda Sarga 34 Shloka 13

वानर O monkey, पूर्वम् in the past, कृतार्थः one whose object is achieved, त्वम् you, यत् since, रामस्य Rama's, न प्रतिकरोषि not helped in return, तत् that, अनार्यः ignoble one, कृतघ्नश्च ungrateful, मिथ्यावादी च one who is a liar, ननु you are surely.

'O monkey you have already achieved your objective (with the help of Rama) but have not helped Rama in return. You are surely an ignoble and ungrateful liar.