Bhagavad Gita 18.48
The duty that falls to one's lot of its own accord should not be abandoned, though it may have its defects. All acts are marred by defects, just as fire is obscured by smoke.
सहजं कर्म कौन्तेय सदोषमपि न त्यजेत्।सर्वारम्भा हि दोषेण धूमेनाग्निरिवावृताः॥sahajaṃ karma kaunteya sadoṣamapi na tyajet|sarvārambhā hi doṣeṇa dhūmenāgnirivāvṛtāḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).