Manusmriti

siva.sh/manusmriti/7/73

यथा दुर्गाश्रितानेतान्नोपहिंसन्ति शत्रवः । तथाऽरयो न हिंसन्ति नृपं दुर्गसमाश्रितम् ॥ ७३ ॥

sanskrit

As enemies do not hurt these (beings, when they are) sheltered by (their) fortresses, even so foes (can) not injure a king who has taken refuge in his fort.

english translation

yathA durgAzritAnetAnnopahiMsanti zatravaH | tathA'rayo na hiMsanti nRpaM durgasamAzritam || 73 ||

hk transliteration by Sanscript