One verse

Srimad Bhagavatam 6.16.27

6.16.27

चित्रकेतुस्तु तां विद्यां यथा नारदभाषिताम् । धारयामास सप्ताहमब्भक्ष: सुसमाहित: ॥ २७ ॥

citraketus tu tam vidyam yatha narada-bhasitam dharayam asa saptaham ab-bhaksah susamahitah

citraketuh
King Citraketu
tu
indeed
tam
that
vidyam
transcendental knowledge
yatha
just as
narada-bhasitam
instructed by the great sage Narada
dharayam asa
chanted
sapta-aham
continuously for one week
ap-bhaksah
only drinking water
su-samahitah
with great attention and care.

Fasting and drinking only water, Citraketu for one week continuously chanted with great care and attention the mantra given by Narada Muni.