One verse

Srimad Bhagavatam 6.2.19

6.2.19

यथागदं वीर्यतममुपयुक्तं यद‍ृच्छया । अजानतोऽप्यात्मगुणं कुर्यान्मन्त्रोऽप्युदाहृत: ॥ १९ ॥

yathagadam viryatamam upayuktam yadrcchaya ajanato ’py atma-gunam kuryan mantro ’py udahrtah

yatha
just like
agadam
medicine
virya-tamam
very powerful
upayuktam
properly taken
yadrcchaya
somehow or other
ajanatah
by a person without knowledge
api
even
atma-gunam
its own potency
kuryat
manifests
mantrah
the Hare Krsna mantra
api
also
udahrtah
chanted.

If a person unaware of the effective potency of a certain medicine takes that medicine or is forced to take it, it will act even without his knowledge because its potency does not depend on the patient’s understanding. Similarly, even though one does not know the value of chanting the holy name of the Lord, if one chants knowingly or unknowingly, the chanting will be very effective.