Manusmriti
पृष्ठतस्तु शरीरस्य नोत्तमाङ्गे कथं चन । अतोऽन्यथा तु प्रहरन् प्राप्तः स्याच्चौरकिल्बिषम् ॥ ३०० ॥
But on the back part of the body (only), never on a noble part; he who strikes them otherwise will incur the same guilt as a thief.
english translation
pRSThatastu zarIrasya nottamAGge kathaM cana । ato'nyathA tu praharan prAptaH syAccaurakilbiSam ॥ 300 ॥
hk transliteration by Sanscript