Mundaka Upanishad, Second Khanda Sanskrit source English source contains some verses that leads to Nishkama Karma.
अविद्यायं बहुधा वर्तमाना वयं कृतार्था इत्यभिमन्यन्ति बालाः ।
यत् कर्मिणो न प्रवेदयन्ति रागात्
तेनातुराः क्षीणलोकाश्च्यवन्ते॥ ९
Children, when they have long lived in ignorance, consider themselves happy. Because those who depend on their good works are, owing to their passions, improvident, they fall and become miserable when their life (in the world which they had gained by their good works) is finished.
इष्टापूर्तं मन्यमाना वरिष्ठं
लोकं हीनतरं वा विशन्ति
Considering sacrifice and good works as the best, these fools know no higher good, and having enjoyed (their reward) on the height of heaven, gained by good works, they enter again this world or a lower one.
Bhagavad Gita, Chapter 5 also contains Shlokas leading to Nishkam Karma (desire-less deeds).
brahmaṇy ādhāya karmāṇi
saṅgaṁ tyaktvā karoti yaḥ
lipyate na sa pāpena
Bg 5.10- One who performs his duty without attachment, surrendering the results unto the Supreme Lord, is unaffected by sinful action, as the lotus leaf is untouched by water.
kāyena manasā buddhyā
kevalair indriyair api
yoginaḥ karma kurvanti
Bg 5.11- The yogīs, abandoning attachment, act with body, mind, intelligence and even with the senses, only for the purpose of puriﬁcation.
Bhagavad Gita, Chapter 12 also talks about renunciation of fruits of action.
śreyo hi jñānam abhyāsāj
jñānād dhyānaṁ viśiṣyate
tyāgāc chāntir anantaram
Bg 12.12- If you cannot take to this practice, then engage yourself in the cultivation of knowledge. Better than knowledge, however, is meditation, and better than meditation is renunciation of the fruits of action, for by such renunciation one can attain peace of mind.