Skanda Purana,
mahabhagavata nityam
kalau smakirtaya kesavam
“The hallmark of a mahabhagavata the most elevated devotee in Kali-yuga is that he chants the holy name of the Lord constantly.”
Linga Purana,
varjams-tisthan svapannasnan
svasan vakya-prapurane
nama-samkirtanam visnor-
helaya kali-vardhanam
krtva svarupatam yati
bhakti-yuktam param vrajet
“In our normal activities of eating, sleeping, sitting, dreaming, etc. to chant Krishna’s names, while nullify the ill effects of Kali-yuga, is the perfection of speech. Even it a person chants Krishna’s names indifferently; he will surely achieve his svarupa, or original spiritual self and attain that state beyond all material fear and lamentation. He will reach Vaikuntha, the supreme goal.”
Kali Santarana Upanisad,
hare Krishna hare Krishna
Krishna Krishna hare hare
hare rama hare rama
rama rama hare hare
iti sodasakam namnam
kali-kalmasa-nasanam
natah parataropayah
sarva-vedesu drsyate
“After searching through all the Vedic literature one cannot find a method of religion more sublime for this age than the chanting of Hare Krishna”
Finally, Madhva himself, quoting Narayana Samhita, in his Mundakopanisad Bhasya says,
dvapariyair janair visnuh
pancaratrais tu kevalam
kalau tu nama-matrena
pujyate bhagavan harih
“In the Dvapara-yuga people should worship Lord Visnu only by the regulative principles of the pancaratra and other such authorized books. In the Age of Kali, however, people should only chant the Holy Names of the Supreme Personality of Godhead.”