Valmiki Ramayana Sundara Kanda Sarga 30 Shloka 17

अहं तु I too, अतितनुश्च small body, विशेषतः more so, वानरश्च a vanara, इह here, सम्स्कृताम् sanskrit language, मानुषीम् of human, वाचं च and talk in, उदाहरिष्यामि I will adopt.

I am indeed of small size and that too a monkey. Nevertheless I shall speak in Sanskrit, a language of the common people. (as the she-demons cannot understand that language).