Ramayana
उपकारेण वीरस्तु प्रतीकारेण युज्यते । अकृतज्ञोऽप्रतिकृतो हन्ति सत्त्ववतां मनः ॥ ४-२८-६४
'A hero should in return help whoever has helped him. An ungrateful person hurts the heart of the virtuous by not returning the assistance.' ॥ 4-28-64॥
english translation
upakAreNa vIrastu pratIkAreNa yujyate । akRtajJo'pratikRto hanti sattvavatAM manaH ॥ 4-28-64
hk transliteration by Sanscript