Valmiki Ramayana Kishkindha Kanda Sarga 2 Shloka 27
Original Shlokaशुद्धात्मानौ यदि त्वेतौ जानीहि त्वं प्लवङ्गम। व्याभाषितैर्वा विज्ञेया स्याद्दुष्टाऽदुष्टता तयोः4.2.27।।
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प्लवङ्गम O best of monkey एतौ they both, शुद्धात्मानौ यदि if they are found trust worthy you, जानीहि you may know, तयोः with them, दुष्टाऽदुष्टता evil minded or otherwise, व्याभाषितैः with their talk, वा or, विजेया should be found out
'O best of monkeys find out whether they are noble in their intentions or evil in their design through your conversation with them.'