One verse

Srimad Bhagavatam 10.3.33

10.3.33

युवां वै ब्रह्मणादिष्टौ प्रजासर्गे यदा तत: । सन्नियम्येन्द्रियग्रामं तेपाथे परमं तप: ॥ ३३ ॥

yuvāṁ vai brahmaṇādiṣṭau prajā-sarge yadā tataḥ sanniyamyendriya-grāmaṁ tepāthe paramaṁ tapaḥ

yuvām
both of you (Pṛśni and Sutapā)
vai
indeed
brahmaṇā ādiṣṭau
ordered by Lord Brahmā (who is known as Pitāmaha, the father of the Prajāpatis)
prajā-sarge
in the creation of progeny
yadā
when
tataḥ
thereafter
sanniyamya
keeping under full control
indriya-grāmam
the senses
tepāthe
underwent
paramam
very great
tapaḥ
austerity

When both of you were ordered by Lord Brahmā to create progeny, you first underwent severe austerities by controlling your senses.