Brihadaranyaka Upanishad 1.3.4

1.3.4

atha ha cakṣurūcustvaṃ na udgāyeti tatheti tebhyaścakṣurudagāyat | yaścakṣuṣi bhogastaṃ devebhya āgāyadyatkalyāṇaṃ paśyati tadātmane | te viduranena vai na udgātrātyeṣyantīti tamabhidrutya pāpmanāvidhyansa yaḥ sa pāpmā yadevedamapratirūpaṃ paśyati sa eva sa pāpmā

Then they said to the eye: 'Do thou sing out for us.' 'Yes,' said the eye, and sang. Whatever delight there is in the eye, that he obtained for the Devas by singing; but that he saw well, that was for himself The Asuras knew: 'Verily, through this singer they will overcome us.' They therefore rushed at the singer, and pierced him with evil. That evil which consists in seeing what is bad, that is that evil.