Valmiki Ramayana Kishkindha Kanda Sarga 4 Shloka 32
Original Shlokaप्रसन्नमुखवर्णश्च व्यक्तं हृष्टश्च भाषते। नानृतं वक्ष्यते वीरो हनुमान्मारुतात्मजः4.4.32।।
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व्यक्तम् it is evident, प्रसन्नमुखवर्णश्च he has a cheerful face, हृष्टश्च he is pleased, भाषते words, मारुतात्मजः son of the windgod, हनुमान् Hanuman, अनृतम् lie, न वक्ष्यते will not tell
'It is evident from his words and from his cheerful face that Hanuman is pleased. (I know that) this heroic son of the Windgod will never tell a lie'.