Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 1.3.3

1.3.3

atha ha prāṇamūcustvaṃ na udgāyeti tatheti tebhyaḥ prāṇa udagāyadyaḥ prāṇe bhogastaṃ devebhya āgāyadyatkalyāṇaṃ jighrati tadātmane te viduranena vai na udgātrātyeṣyantīti tamabhidrutya pāpmanāvidhyansa yaḥ sa papmā yadevedamapratirūpaṃ jighrati sa eva sa pāpmā

Then they (the Devas) said to breath (scent): 'Do thou sing out for us.' 'Yes,' said breath, and sang. Whatever delight there is in breath (smell), that he obtained for the Devas by singing; but that he smelled 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 smelling what is bad, that is that evil.