SB 3.20.49

sa ātmānaṁ manyamānaḥ
 kṛta-kṛtyam ivātmabhūḥ
tadā manūn sasarjānte
 manasā loka-bhāvanān
Synonyms: 
saḥ — Lord Brahmā; ātmānam — himself; manyamānaḥ — considering; kṛta-kṛtyam — had accomplished the object of life; iva — as if; ātmabhūḥ — born from the Supreme; tadā — then; manūn — the Manus; sasarja — created; ante — at the end; manasā — from his mind; loka — of the world; bhāvanān — promoting the welfare.
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.