Valmiki Ramayana Kishkindha Kanda Sarga 18 Shloka 43

तान् them, न हिंस्यात् insult, न चाक्रोशेत् not to be shouted, न आक्षिपेत् not to be disregarded, अप्रियम् unpleasant, न वदेत् not speak, एते they, देवाः gods, मानुषरूपेण in the form of human beings, महीतले on this earth, चरन्ति move about.

'One should not insult kings, nor shout at them, nor disregard them nor speak unpleasant words to them. They are gods in human form moving on this earth.