One verse

Srimad Bhagavatam 4.8.58

4.8.58

परिचर्या भगवतो यावत्य: पूर्वसेविता: । ता मन्त्रहृदयेनैव प्रयुञ्‍ज्यान्मन्त्रमूर्तये ॥ ५८ ॥

paricarya bhagavato yavatyah purva-sevitah ta mantra-hrdayenaiva prayunjyan mantra-murtaye

paricaryah
service
bhagavatah
of the Personality of Godhead
yavatyah
as they are prescribed (as above mentioned)
purva-sevitah
recommended or done by previous acaryas
tah
that
mantra
hymns
hrdayena
within the heart
eva
certainly
prayunjyat
one should worship
mantra-murtaye
who is nondifferent from the mantra.

One should follow in the footsteps of previous devotees regarding how to worship the Supreme Lord with the prescribed paraphernalia, or one should offer worship within the heart by reciting the mantra to the Personality of Godhead, who is nondifferent from the mantra.