One verse

Srimad Bhagavatam 7.10.4

7.10.4

नान्यथा तेऽखिलगुरो घटेत करुणात्मन: । यस्त आशिष आशास्ते न स भृत्य: स वै वणिक् ॥ ४ ॥

nanyatha te ’khila-guro ghateta karunatmanah yas ta asisa asaste na sa bhrtyah sa vai vanik

na
not
anyatha
otherwise
te
of You
akhila-guro
O supreme instructor of the entire creation
ghateta
such a thing can happen
karuna-atmanah
the Supreme Person, who is extremely kind to His devotees
yah
any person who
te
from You
asisah
material benefits
asaste
desires (in exchange for serving You)
na
not
sah
such a person
bhrtyah
a servitor
sah
such a person
vai
indeed
vanik
a merchant (who wants to get material profit from his business)

Otherwise, O my Lord, O supreme instructor of the entire world, You are so kind to Your devotee that You could not induce him to do something unbeneficial for him. On the other hand, one who desires some material benefit in exchange for devotional service cannot be Your pure devotee. Indeed, he is no better than a merchant who wants profit in exchange for service.