Valmiki Ramayana Kishkindha Kanda Sarga 3 Shloka 29

नूनम् surely, अनेन by him, कृत्स्नम् entire, व्याकरणम् grammar, बहुधा in many ways, श्रुतम् studied, बहु much, व्याहरता spoken, अनेन by him, किञ्चित् even a little, अपशब्दितम् wrong pronunciation

'Surely, he seems to have studied well the whole of grammar, for there is not a single mispronunciation in his entire speech.