SB 10.85.47

śrī-bhagavān uvāca
āsan marīceḥ ṣaṭ putrā
 ūrṇāyāṁ prathame ’ntare
devāḥ kaṁ jahasur vīkṣya
 sutaṁ yabhitum udyatam
Synonyms: 
śrī-bhagavān uvāca — the Supreme Lord said; āsan — there were; marīceḥ — of Marīci; ṣaṭ — six; putrāḥ — sons; ūrṇāyām — born of Ūrṇā (his wife); prathame — in the first; antare — rule of Manu; devāḥ — demigods; kam — at Lord Brahmā; jahasuḥ — they laughed; vīkṣya — seeing; sutām — with his daughter (Sarasvatī); yabhitum — to copulate; udyatam — prepared.
Translation: 
The Supreme Lord said: During the age of the first Manu, the sage Marīci had six sons by his wife Ūrnā. They were all exalted demigods, but once they laughed at Lord Brahmā when they saw him preparing to have sex with his own daughter.