Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 49
Sanskrit:
स आत्मान् मन्यमान: कृतकृत्यमिवात्मभू: ।तदा मनून् ससर्जान्ते मनसा लोकभावनान् ॥ ४९ ॥
ITRANS:
sa ātmānaṁ manyamānaḥkṛta-kṛtyam ivātmabhūḥtadā manūn sasarjāntemanasā loka-bhāvanān
Translation:
One day Brahmā, the self-born, the first living creature, felt as if the object of his life had been accomplished. At that time he evolved from his mind the Manus, who promote the welfare activities of the universe.