Srimad Bhagavatam Canto 08, Chapter 16, Text 25

SB 8.16.25

phalgunasyamale pakse
 dvadasaham payo-vratam
arcayed aravindaksam
 bhaktya paramayanvitah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
In the bright fortnight of the month of Phalguna [February and March], for twelve days ending with Dvadasi, one should observe the vow of subsisting only on milk and should worship the lotus-eyed Supreme Personality of Godhead with all devotion.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Worshiping the Supreme Lord Visnu with devotion means following arcana-marga.
 
sravanam kirtanam visnoh
 smaranam pada-sevanam
arcanam vandanam dasyam
 sakhyam atma-nivedanam
 
One should install the Deity of Lord Visnu or Krsna and worship Him nicely by dressing Him, decorating Him with flower garlands, and offering Him all kinds of fruits, flowers and cooked food, nicely prepared with ghee, sugar and grains. One should also offer a flame, incense and so on, while ringing a bell, as prescribed. This is called worship of the Lord. Here it is recommended that one observe the vow of subsisting only by drinking milk. This is called payo-vrata. As we generally perform devotional service on Ekadasi by not eating grains, it is generally recommended that on Dvadasi one not consume anything but milk. Payo-vrata and arcana devotional service to the Supreme Lord should be performed with a pure devotional attitude (bhaktya). Without bhakti, one cannot worship the Supreme Personality of Godhead. Bhaktya mam abhijanati yavan yas casmi tattvatah. If one wants to know the Supreme Personality of Godhead and be directly connected with Him, knowing what He wants to eat and how He is satisfied, one must take to the process of bhakti. As recommended here also, bhaktya paramayanvitah: one should be surcharged with unalloyed devotional service.
Srimad Bhagavatam Canto 08, Chapter 16, Text 24
Srimad Bhagavatam Canto 08, Chapter 16, Text 26