Srimad Bhagavatam Canto 04, Chapter 24, Text 32

 SB 4.24.32

maitreya uvaca
ity anukrosa-hrdayo
 bhagavan aha tañ chivah
baddhañjalin raja-putran
 narayana-paro vacah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The great sage Maitreya continued: Out of his causeless mercy, the exalted personality Lord Siva, a great devotee of Lord Narayana, continued to speak to the King’s sons, who were standing with folded hands.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Lord Siva voluntarily came to bless the sons of the King as well as do something beneficial for them. He personally chanted the mantra so that the mantra would be more powerful, and he advised that the mantra be chanted by the King’s sons (raja-putras). When a mantra is chanted by a great devotee, the mantra becomes more powerful. Although the Hare Krsna maha-mantra is powerful in itself, a disciple upon initiation receives the mantra from his spiritual master, for when the mantra is chanted by the spiritual master, it becomes more powerful. Lord Siva advised the sons of the King to hear him attentively, for inattentive hearing is offensive.
Srimad Bhagavatam Canto 04, Chapter 24, Text 31
Srimad Bhagavatam Canto 04, Chapter 24, Text 33