One verse

Srimad Bhagavatam 8.16.46

8.16.46

पयोभक्षो व्रतमिदं चरेद् विष्णवर्चनाद‍ृत: । पूर्ववज्जुहुयादग्निं ब्राह्मणांश्चापि भोजयेत् ॥ ४६ ॥

payo-bhakso vratam idam cared visnv-arcanadrtah purvavaj juhuyad agnim brahmanams capi bhojayet

payah-bhaksah
one who drinks milk only
vratam idam
this process of worshiping with a vow
caret
one should execute
visnu-arcana-adrtah
worshiping Lord Visnu with great faith and devotion
purva-vat
as prescribed previously
juhuyat
one should offer oblations
agnim
into the fire
brahmanan
unto the brahmanas
ca api
as well as
bhojayet
should feed.

Worshiping Lord Visnu with great faith and devotion and living only by drinking milk, one should follow this vow. One should also offer oblations to the fire and feed the brahmanas as mentioned before.